/*!
 * reveal.js
 * http://lab.hakim.se/reveal-js
 * MIT licensed
 *
 * Copyright (C) 2015 Hakim El Hattab, http://hakim.se
 */
(function( root, factory ) {
  if( typeof define === 'function' && define.amd ) {
    // AMD. Register as an anonymous module.
    define( function() {
      root.Reveal = factory();
      return root.Reveal;
    } );
  } else if( typeof exports === 'object' ) {
    // Node. Does not work with strict CommonJS.
    module.exports = factory();
  } else {
    // Browser globals.
    root.Reveal = factory();
  }
}( this, function() {

  'use strict';

  var Reveal;

  var SLIDES_SELECTOR = '.slides section',
    HORIZONTAL_SLIDES_SELECTOR = '.slides>section',
    VERTICAL_SLIDES_SELECTOR = '.slides>section.present>section',
    HOME_SLIDE_SELECTOR = '.slides>section:first-of-type',

    // Configuration defaults, can be overridden at initialization time
    config = {

      // The "normal" size of the presentation, aspect ratio will be preserved
      // when the presentation is scaled to fit different resolutions
      width: 960,
      height: 700,

      // Factor of the display size that should remain empty around the content
      margin: 0.1,

      // Bounds for smallest/largest possible scale to apply to content
      minScale: 0.2,
      maxScale: 1.5,

      // Display controls in the bottom right corner
      controls: true,

      // Display a presentation progress bar
      progress: true,

      // Display the page number of the current slide
      slideNumber: false,

      // Push each slide change to the browser history
      history: false,

      // Enable keyboard shortcuts for navigation
      keyboard: true,

      // Optional function that blocks keyboard events when retuning false
      keyboardCondition: null,

      // Enable the slide overview mode
      overview: true,

      // Vertical centering of slides
      center: true,

      // Enables touch navigation on devices with touch input
      touch: true,

      // Loop the presentation
      loop: false,

      // Change the presentation direction to be RTL
      rtl: false,

      // Turns fragments on and off globally
      fragments: true,

      // Flags if the presentation is running in an embedded mode,
      // i.e. contained within a limited portion of the screen
      embedded: false,

      // Flags if we should show a help overlay when the questionmark
      // key is pressed
      help: true,

      // Flags if it should be possible to pause the presentation (blackout)
      pause: true,

      // Number of milliseconds between automatically proceeding to the
      // next slide, disabled when set to 0, this value can be overwritten
      // by using a data-autoslide attribute on your slides
      autoSlide: 0,

      // Stop auto-sliding after user input
      autoSlideStoppable: true,

      // Enable slide navigation via mouse wheel
      mouseWheel: false,

      // Apply a 3D roll to links on hover
      rollingLinks: false,

      // Hides the address bar on mobile devices
      hideAddressBar: true,

      // Opens links in an iframe preview overlay
      previewLinks: false,

      // Exposes the reveal.js API through window.postMessage
      postMessage: true,

      // Dispatches all reveal.js events to the parent window through postMessage
      postMessageEvents: false,

      // Focuses body when page changes visiblity to ensure keyboard shortcuts work
      focusBodyOnPageVisibilityChange: true,

      // Transition style
      transition: 'slide', // none/fade/slide/convex/concave/zoom

      // Transition speed
      transitionSpeed: 'default', // default/fast/slow

      // Transition style for full page slide backgrounds
      backgroundTransition: 'fade', // none/fade/slide/convex/concave/zoom

      // Parallax background image
      parallaxBackgroundImage: '', // CSS syntax, e.g. "a.jpg"

      // Parallax background size
      parallaxBackgroundSize: '', // CSS syntax, e.g. "3000px 2000px"

      // Amount of pixels to move the parallax background per slide step
      parallaxBackgroundHorizontal: null,
      parallaxBackgroundVertical: null,

      // Number of slides away from the current that are visible
      viewDistance: 3,

      // Script dependencies to load
      dependencies: []

    },

    // Flags if reveal.js is loaded (has dispatched the 'ready' event)
    loaded = false,

    // Flags if the overview mode is currently active
    overview = false,

    // The horizontal and vertical index of the currently active slide
    indexh,
    indexv,

    // The previous and current slide HTML elements
    previousSlide,
    currentSlide,

    previousBackground,

    // Slides may hold a data-state attribute which we pick up and apply
    // as a class to the body. This list contains the combined state of
    // all current slides.
    state = [],

    // The current scale of the presentation (see width/height config)
    scale = 1,

    // CSS transform that is currently applied to the slides container,
    // split into two groups
    slidesTransform = { layout: '', overview: '' },

    // Cached references to DOM elements
    dom = {},

    // Features supported by the browser, see #checkCapabilities()
    features = {},

    // Client is a mobile device, see #checkCapabilities()
    isMobileDevice,

    // Throttles mouse wheel navigation
    lastMouseWheelStep = 0,

    // Delays updates to the URL due to a Chrome thumbnailer bug
    writeURLTimeout = 0,

    // Flags if the interaction event listeners are bound
    eventsAreBound = false,

    // The current auto-slide duration
    autoSlide = 0,

    // Auto slide properties
    autoSlidePlayer,
    autoSlideTimeout = 0,
    autoSlideStartTime = -1,
    autoSlidePaused = false,

    // Holds information about the currently ongoing touch input
    touch = {
      startX: 0,
      startY: 0,
      startSpan: 0,
      startCount: 0,
      captured: false,
      threshold: 40
    },

    // Holds information about the keyboard shortcuts
    keyboardShortcuts = {
      'N  ,  SPACE':      'Next slide',
      'P':          'Previous slide',
      '&#8592;  ,  H':    'Navigate left',
      '&#8594;  ,  L':    'Navigate right',
      '&#8593;  ,  K':    'Navigate up',
      '&#8595;  ,  J':    'Navigate down',
      'Home':         'First slide',
      'End':          'Last slide',
      'B  ,  .':        'Pause',
      'F':          'Fullscreen',
      'ESC, O':       'Slide overview'
    };

  /**
   * Starts up the presentation if the client is capable.
   */
  function initialize( options ) {

    checkCapabilities();

    if( !features.transforms2d && !features.transforms3d ) {
      document.body.setAttribute( 'class', 'no-transforms' );

      // Since JS won't be running any further, we load all lazy
      // loading elements upfront
      var images = toArray( document.getElementsByTagName( 'img' ) ),
        iframes = toArray( document.getElementsByTagName( 'iframe' ) );

      var lazyLoadable = images.concat( iframes );

      for( var i = 0, len = lazyLoadable.length; i < len; i++ ) {
        var element = lazyLoadable[i];
        if( element.getAttribute( 'data-src' ) ) {
          element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
          element.removeAttribute( 'data-src' );
        }
      }

      // If the browser doesn't support core features we won't be
      // using JavaScript to control the presentation
      return;
    }

    // Cache references to key DOM elements
    dom.wrapper = document.querySelector( '.reveal' );
    dom.slides = document.querySelector( '.reveal .slides' );

    // Force a layout when the whole page, incl fonts, has loaded
    window.addEventListener( 'load', layout, false );

    var query = Reveal.getQueryHash();

    // Do not accept new dependencies via query config to avoid
    // the potential of malicious script injection
    if( typeof query['dependencies'] !== 'undefined' ) delete query['dependencies'];

    // Copy options over to our config object
    extend( config, options );
    extend( config, query );

    // Hide the address bar in mobile browsers
    hideAddressBar();

    // Loads the dependencies and continues to #start() once done
    load();

  }

  /**
   * Inspect the client to see what it's capable of, this
   * should only happens once per runtime.
   */
  function checkCapabilities() {

    features.transforms3d = 'WebkitPerspective' in document.body.style ||
                'MozPerspective' in document.body.style ||
                'msPerspective' in document.body.style ||
                'OPerspective' in document.body.style ||
                'perspective' in document.body.style;

    features.transforms2d = 'WebkitTransform' in document.body.style ||
                'MozTransform' in document.body.style ||
                'msTransform' in document.body.style ||
                'OTransform' in document.body.style ||
                'transform' in document.body.style;

    features.requestAnimationFrameMethod = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame;
    features.requestAnimationFrame = typeof features.requestAnimationFrameMethod === 'function';

    features.canvas = !!document.createElement( 'canvas' ).getContext;

    features.touch = !!( 'ontouchstart' in window );

    // Transitions in the overview are disabled in desktop and
    // mobile Safari due to lag
    features.overviewTransitions = !/Version\/[\d\.]+.*Safari/.test( navigator.userAgent );

    isMobileDevice = /(iphone|ipod|ipad|android)/gi.test( navigator.userAgent );

  }

    /**
     * Loads the dependencies of reveal.js. Dependencies are
     * defined via the configuration option 'dependencies'
     * and will be loaded prior to starting/binding reveal.js.
     * Some dependencies may have an 'async' flag, if so they
     * will load after reveal.js has been started up.
     */
  function load() {

    var scripts = [],
      scriptsAsync = [],
      scriptsToPreload = 0;

    // Called once synchronous scripts finish loading
    function proceed() {
      if( scriptsAsync.length ) {
        // Load asynchronous scripts
        head.js.apply( null, scriptsAsync );
      }

      start();
    }

    function loadScript( s ) {
      head.ready( s.src.match( /([\w\d_\-]*)\.?js$|[^\\\/]*$/i )[0], function() {
        // Extension may contain callback functions
        if( typeof s.callback === 'function' ) {
          s.callback.apply( this );
        }

        if( --scriptsToPreload === 0 ) {
          proceed();
        }
      });
    }

    for( var i = 0, len = config.dependencies.length; i < len; i++ ) {
      var s = config.dependencies[i];

      // Load if there's no condition or the condition is truthy
      if( !s.condition || s.condition() ) {
        if( s.async ) {
          scriptsAsync.push( s.src );
        }
        else {
          scripts.push( s.src );
        }

        loadScript( s );
      }
    }

    if( scripts.length ) {
      scriptsToPreload = scripts.length;

      // Load synchronous scripts
      head.js.apply( null, scripts );
    }
    else {
      proceed();
    }

  }

  /**
   * Starts up reveal.js by binding input events and navigating
   * to the current URL deeplink if there is one.
   */
  function start() {

    // Make sure we've got all the DOM elements we need
    setupDOM();

    // Listen to messages posted to this window
    setupPostMessage();

    // Prevent iframes from scrolling the slides out of view
    setupIframeScrollPrevention();

    // Resets all vertical slides so that only the first is visible
    resetVerticalSlides();

    // Updates the presentation to match the current configuration values
    configure();

    // Read the initial hash
    readURL();

    // Update all backgrounds
    updateBackground( true );

    // Notify listeners that the presentation is ready but use a 1ms
    // timeout to ensure it's not fired synchronously after #initialize()
    setTimeout( function() {
      // Enable transitions now that we're loaded
      dom.slides.classList.remove( 'no-transition' );

      loaded = true;

      dispatchEvent( 'ready', {
        'indexh': indexh,
        'indexv': indexv,
        'currentSlide': currentSlide
      } );
    }, 1 );

    // Special setup and config is required when printing to PDF
    if( isPrintingPDF() ) {
      removeEventListeners();

      // The document needs to have loaded for the PDF layout
      // measurements to be accurate
      if( document.readyState === 'complete' ) {
        setupPDF();
      }
      else {
        window.addEventListener( 'load', setupPDF );
      }
    }

  }

  /**
   * Finds and stores references to DOM elements which are
   * required by the presentation. If a required element is
   * not found, it is created.
   */
  function setupDOM() {

    // Prevent transitions while we're loading
    dom.slides.classList.add( 'no-transition' );

    // Background element
    dom.background = createSingletonNode( dom.wrapper, 'div', 'backgrounds', null );

    // Progress bar
    dom.progress = createSingletonNode( dom.wrapper, 'div', 'progress', '<span></span>' );
    dom.progressbar = dom.progress.querySelector( 'span' );

    // Arrow controls
    createSingletonNode( dom.wrapper, 'aside', 'controls',
      '<div class="navigate-left"></div>' +
      '<div class="navigate-right"></div>' +
      '<div class="navigate-up"></div>' +
      '<div class="navigate-down"></div>' );

    // Slide number
    dom.slideNumber = createSingletonNode( dom.wrapper, 'div', 'slide-number', '' );

    // Overlay graphic which is displayed during the paused mode
    createSingletonNode( dom.wrapper, 'div', 'pause-overlay', null );

    // Cache references to elements
    dom.controls = document.querySelector( '.reveal .controls' );
    dom.theme = document.querySelector( '#theme' );

    dom.wrapper.setAttribute( 'role', 'application' );

    // There can be multiple instances of controls throughout the page
    dom.controlsLeft = toArray( document.querySelectorAll( '.navigate-left' ) );
    dom.controlsRight = toArray( document.querySelectorAll( '.navigate-right' ) );
    dom.controlsUp = toArray( document.querySelectorAll( '.navigate-up' ) );
    dom.controlsDown = toArray( document.querySelectorAll( '.navigate-down' ) );
    dom.controlsPrev = toArray( document.querySelectorAll( '.navigate-prev' ) );
    dom.controlsNext = toArray( document.querySelectorAll( '.navigate-next' ) );

    dom.statusDiv = createStatusDiv();
  }

  /**
   * Creates a hidden div with role aria-live to announce the
   * current slide content. Hide the div off-screen to make it
   * available only to Assistive Technologies.
   */
  function createStatusDiv() {

    var statusDiv = document.getElementById( 'aria-status-div' );
    if( !statusDiv ) {
      statusDiv = document.createElement( 'div' );
      statusDiv.style.position = 'absolute';
      statusDiv.style.height = '1px';
      statusDiv.style.width = '1px';
      statusDiv.style.overflow ='hidden';
      statusDiv.style.clip = 'rect( 1px, 1px, 1px, 1px )';
      statusDiv.setAttribute( 'id', 'aria-status-div' );
      statusDiv.setAttribute( 'aria-live', 'polite' );
      statusDiv.setAttribute( 'aria-atomic','true' );
      dom.wrapper.appendChild( statusDiv );
    }
    return statusDiv;

  }

  /**
   * Configures the presentation for printing to a static
   * PDF.
   */
  function setupPDF() {

    var slideSize = getComputedSlideSize( window.innerWidth, window.innerHeight );

    // Dimensions of the PDF pages
    var pageWidth = Math.floor( slideSize.width * ( 1 + config.margin ) ),
      pageHeight = Math.floor( slideSize.height * ( 1 + config.margin  ) );

    // Dimensions of slides within the pages
    var slideWidth = slideSize.width,
      slideHeight = slideSize.height;

    // Let the browser know what page size we want to print
    injectStyleSheet( '@page{size:'+ pageWidth +'px '+ pageHeight +'px; margin: 0;}' );

    // Limit the size of certain elements to the dimensions of the slide
    injectStyleSheet( '.reveal section>img, .reveal section>video, .reveal section>iframe{max-width: '+ slideWidth +'px; max-height:'+ slideHeight +'px}' );

    document.body.classList.add( 'print-pdf' );
    document.body.style.width = pageWidth + 'px';
    document.body.style.height = pageHeight + 'px';

    // Slide and slide background layout
    toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {

      // Vertical stacks are not centred since their section
      // children will be
      if( slide.classList.contains( 'stack' ) === false ) {
        // Center the slide inside of the page, giving the slide some margin
        var left = ( pageWidth - slideWidth ) / 2,
          top = ( pageHeight - slideHeight ) / 2;

        var contentHeight = getAbsoluteHeight( slide );
        var numberOfPages = Math.max( Math.ceil( contentHeight / pageHeight ), 1 );

        // Center slides vertically
        if( numberOfPages === 1 && config.center || slide.classList.contains( 'center' ) ) {
          top = Math.max( ( pageHeight - contentHeight ) / 2, 0 );
        }

        // Position the slide inside of the page
        slide.style.left = left + 'px';
        slide.style.top = top + 'px';
        slide.style.width = slideWidth + 'px';

        // TODO Backgrounds need to be multiplied when the slide
        // stretches over multiple pages
        var background = slide.querySelector( '.slide-background' );
        if( background ) {
          background.style.width = pageWidth + 'px';
          background.style.height = ( pageHeight * numberOfPages ) + 'px';
          background.style.top = -top + 'px';
          background.style.left = -left + 'px';
        }
      }

    } );

    // Show all fragments
    toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' .fragment' ) ).forEach( function( fragment ) {
      fragment.classList.add( 'visible' );
    } );

  }

  /**
   * This is an unfortunate necessity. Iframes can trigger the
   * parent window to scroll, for example by focusing an input.
   * This scrolling can not be prevented by hiding overflow in
   * CSS so we have to resort to repeatedly checking if the
   * browser has decided to offset our slides :(
   */
  function setupIframeScrollPrevention() {

    if( dom.slides.querySelector( 'iframe' ) ) {
      setInterval( function() {
        if( dom.wrapper.scrollTop !== 0 || dom.wrapper.scrollLeft !== 0 ) {
          dom.wrapper.scrollTop = 0;
          dom.wrapper.scrollLeft = 0;
        }
      }, 500 );
    }

  }

  /**
   * Creates an HTML element and returns a reference to it.
   * If the element already exists the existing instance will
   * be returned.
   */
  function createSingletonNode( container, tagname, classname, innerHTML ) {

    // Find all nodes matching the description
    var nodes = container.querySelectorAll( '.' + classname );

    // Check all matches to find one which is a direct child of
    // the specified container
    for( var i = 0; i < nodes.length; i++ ) {
      var testNode = nodes[i];
      if( testNode.parentNode === container ) {
        return testNode;
      }
    }

    // If no node was found, create it now
    var node = document.createElement( tagname );
    node.classList.add( classname );
    if( typeof innerHTML === 'string' ) {
      node.innerHTML = innerHTML;
    }
    container.appendChild( node );

    return node;

  }

  /**
   * Creates the slide background elements and appends them
   * to the background container. One element is created per
   * slide no matter if the given slide has visible background.
   */
  function createBackgrounds() {

    var printMode = isPrintingPDF();

    // Clear prior backgrounds
    dom.background.innerHTML = '';
    dom.background.classList.add( 'no-transition' );

    // Iterate over all horizontal slides
    toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( slideh ) {

      var backgroundStack;

      if( printMode ) {
        backgroundStack = createBackground( slideh, slideh );
      }
      else {
        backgroundStack = createBackground( slideh, dom.background );
      }

      // Iterate over all vertical slides
      toArray( slideh.querySelectorAll( 'section' ) ).forEach( function( slidev ) {

        if( printMode ) {
          createBackground( slidev, slidev );
        }
        else {
          createBackground( slidev, backgroundStack );
        }

        backgroundStack.classList.add( 'stack' );

      } );

    } );

    // Add parallax background if specified
    if( config.parallaxBackgroundImage ) {

      dom.background.style.backgroundImage = 'url("' + config.parallaxBackgroundImage + '")';
      dom.background.style.backgroundSize = config.parallaxBackgroundSize;

      // Make sure the below properties are set on the element - these properties are
      // needed for proper transitions to be set on the element via CSS. To remove
      // annoying background slide-in effect when the presentation starts, apply
      // these properties after short time delay
      setTimeout( function() {
        dom.wrapper.classList.add( 'has-parallax-background' );
      }, 1 );

    }
    else {

      dom.background.style.backgroundImage = '';
      dom.wrapper.classList.remove( 'has-parallax-background' );

    }

  }

  /**
   * Creates a background for the given slide.
   *
   * @param {HTMLElement} slide
   * @param {HTMLElement} container The element that the background
   * should be appended to
   */
  function createBackground( slide, container ) {

    var data = {
      background: slide.getAttribute( 'data-background' ),
      backgroundSize: slide.getAttribute( 'data-background-size' ),
      backgroundImage: slide.getAttribute( 'data-background-image' ),
      backgroundVideo: slide.getAttribute( 'data-background-video' ),
      backgroundIframe: slide.getAttribute( 'data-background-iframe' ),
      backgroundColor: slide.getAttribute( 'data-background-color' ),
      backgroundRepeat: slide.getAttribute( 'data-background-repeat' ),
      backgroundPosition: slide.getAttribute( 'data-background-position' ),
      backgroundTransition: slide.getAttribute( 'data-background-transition' )
    };

    var element = document.createElement( 'div' );

    // Carry over custom classes from the slide to the background
    element.className = 'slide-background ' + slide.className.replace( /present|past|future/, '' );

    if( data.background ) {
      // Auto-wrap image urls in url(...)
      if( /^(http|file|\/\/)/gi.test( data.background ) || /\.(svg|png|jpg|jpeg|gif|bmp)$/gi.test( data.background ) ) {
        slide.setAttribute( 'data-background-image', data.background );
      }
      else {
        element.style.background = data.background;
      }
    }

    // Create a hash for this combination of background settings.
    // This is used to determine when two slide backgrounds are
    // the same.
    if( data.background || data.backgroundColor || data.backgroundImage || data.backgroundVideo || data.backgroundIframe ) {
      element.setAttribute( 'data-background-hash', data.background +
                              data.backgroundSize +
                              data.backgroundImage +
                              data.backgroundVideo +
                              data.backgroundIframe +
                              data.backgroundColor +
                              data.backgroundRepeat +
                              data.backgroundPosition +
                              data.backgroundTransition );
    }

    // Additional and optional background properties
    if( data.backgroundSize ) element.style.backgroundSize = data.backgroundSize;
    if( data.backgroundColor ) element.style.backgroundColor = data.backgroundColor;
    if( data.backgroundRepeat ) element.style.backgroundRepeat = data.backgroundRepeat;
    if( data.backgroundPosition ) element.style.backgroundPosition = data.backgroundPosition;
    if( data.backgroundTransition ) element.setAttribute( 'data-background-transition', data.backgroundTransition );

    container.appendChild( element );

    // If backgrounds are being recreated, clear old classes
    slide.classList.remove( 'has-dark-background' );
    slide.classList.remove( 'has-light-background' );

    // If this slide has a background color, add a class that
    // signals if it is light or dark. If the slide has no background
    // color, no class will be set
    var computedBackgroundColor = window.getComputedStyle( element ).backgroundColor;
    if( computedBackgroundColor ) {
      var rgb = colorToRgb( computedBackgroundColor );

      // Ignore fully transparent backgrounds. Some browsers return
      // rgba(0,0,0,0) when reading the computed background color of
      // an element with no background
      if( rgb && rgb.a !== 0 ) {
        if( colorBrightness( computedBackgroundColor ) < 128 ) {
          slide.classList.add( 'has-dark-background' );
        }
        else {
          slide.classList.add( 'has-light-background' );
        }
      }
    }

    return element;

  }

  /**
   * Registers a listener to postMessage events, this makes it
   * possible to call all reveal.js API methods from another
   * window. For example:
   *
   * revealWindow.postMessage( JSON.stringify({
   *   method: 'slide',
   *   args: [ 2 ]
   * }), '*' );
   */
  function setupPostMessage() {

    if( config.postMessage ) {
      window.addEventListener( 'message', function ( event ) {
        var data = event.data;

        // Make sure we're dealing with JSON
        if( typeof data === 'string' && data.charAt( 0 ) === '{' && data.charAt( data.length - 1 ) === '}' ) {
          data = JSON.parse( data );

          // Check if the requested method can be found
          if( data.method && typeof Reveal[data.method] === 'function' ) {
            Reveal[data.method].apply( Reveal, data.args );
          }
        }
      }, false );
    }

  }

  /**
   * Applies the configuration settings from the config
   * object. May be called multiple times.
   */
  function configure( options ) {

    var numberOfSlides = dom.wrapper.querySelectorAll( SLIDES_SELECTOR ).length;

    dom.wrapper.classList.remove( config.transition );

    // New config options may be passed when this method
    // is invoked through the API after initialization
    if( typeof options === 'object' ) extend( config, options );

    // Force linear transition based on browser capabilities
    if( features.transforms3d === false ) config.transition = 'linear';

    dom.wrapper.classList.add( config.transition );

    dom.wrapper.setAttribute( 'data-transition-speed', config.transitionSpeed );
    dom.wrapper.setAttribute( 'data-background-transition', config.backgroundTransition );

    dom.controls.style.display = config.controls ? 'block' : 'none';
    dom.progress.style.display = config.progress ? 'block' : 'none';

    if( config.rtl ) {
      dom.wrapper.classList.add( 'rtl' );
    }
    else {
      dom.wrapper.classList.remove( 'rtl' );
    }

    if( config.center ) {
      dom.wrapper.classList.add( 'center' );
    }
    else {
      dom.wrapper.classList.remove( 'center' );
    }

    // Exit the paused mode if it was configured off
    if( config.pause === false ) {
      resume();
    }

    if( config.mouseWheel ) {
      document.addEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
      document.addEventListener( 'mousewheel', onDocumentMouseScroll, false );
    }
    else {
      document.removeEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
      document.removeEventListener( 'mousewheel', onDocumentMouseScroll, false );
    }

    // Rolling 3D links
    if( config.rollingLinks ) {
      enableRollingLinks();
    }
    else {
      disableRollingLinks();
    }

    // Iframe link previews
    if( config.previewLinks ) {
      enablePreviewLinks();
    }
    else {
      disablePreviewLinks();
      enablePreviewLinks( '[data-preview-link]' );
    }

    // Remove existing auto-slide controls
    if( autoSlidePlayer ) {
      autoSlidePlayer.destroy();
      autoSlidePlayer = null;
    }

    // Generate auto-slide controls if needed
    if( numberOfSlides > 1 && config.autoSlide && config.autoSlideStoppable && features.canvas && features.requestAnimationFrame ) {
      autoSlidePlayer = new Playback( dom.wrapper, function() {
        return Math.min( Math.max( ( Date.now() - autoSlideStartTime ) / autoSlide, 0 ), 1 );
      } );

      autoSlidePlayer.on( 'click', onAutoSlidePlayerClick );
      autoSlidePaused = false;
    }

    // When fragments are turned off they should be visible
    if( config.fragments === false ) {
      toArray( dom.slides.querySelectorAll( '.fragment' ) ).forEach( function( element ) {
        element.classList.add( 'visible' );
        element.classList.remove( 'current-fragment' );
      } );
    }

    sync();

  }

  /**
   * Binds all event listeners.
   */
  function addEventListeners() {

    eventsAreBound = true;

    window.addEventListener( 'hashchange', onWindowHashChange, false );
    window.addEventListener( 'resize', onWindowResize, false );

    if( config.touch ) {
      dom.wrapper.addEventListener( 'touchstart', onTouchStart, false );
      dom.wrapper.addEventListener( 'touchmove', onTouchMove, false );
      dom.wrapper.addEventListener( 'touchend', onTouchEnd, false );

      // Support pointer-style touch interaction as well
      if( window.navigator.pointerEnabled ) {
        // IE 11 uses un-prefixed version of pointer events
        dom.wrapper.addEventListener( 'pointerdown', onPointerDown, false );
        dom.wrapper.addEventListener( 'pointermove', onPointerMove, false );
        dom.wrapper.addEventListener( 'pointerup', onPointerUp, false );
      }
      else if( window.navigator.msPointerEnabled ) {
        // IE 10 uses prefixed version of pointer events
        dom.wrapper.addEventListener( 'MSPointerDown', onPointerDown, false );
        dom.wrapper.addEventListener( 'MSPointerMove', onPointerMove, false );
        dom.wrapper.addEventListener( 'MSPointerUp', onPointerUp, false );
      }
    }

    if( config.keyboard ) {
      document.addEventListener( 'keydown', onDocumentKeyDown, false );
      document.addEventListener( 'keypress', onDocumentKeyPress, false );
    }

    if( config.progress && dom.progress ) {
      dom.progress.addEventListener( 'click', onProgressClicked, false );
    }

    if( config.focusBodyOnPageVisibilityChange ) {
      var visibilityChange;

      if( 'hidden' in document ) {
        visibilityChange = 'visibilitychange';
      }
      else if( 'msHidden' in document ) {
        visibilityChange = 'msvisibilitychange';
      }
      else if( 'webkitHidden' in document ) {
        visibilityChange = 'webkitvisibilitychange';
      }

      if( visibilityChange ) {
        document.addEventListener( visibilityChange, onPageVisibilityChange, false );
      }
    }

    // Listen to both touch and click events, in case the device
    // supports both
    var pointerEvents = [ 'touchstart', 'click' ];

    // Only support touch for Android, fixes double navigations in
    // stock browser
    if( navigator.userAgent.match( /android/gi ) ) {
      pointerEvents = [ 'touchstart' ];
    }

    pointerEvents.forEach( function( eventName ) {
      dom.controlsLeft.forEach( function( el ) { el.addEventListener( eventName, onNavigateLeftClicked, false ); } );
      dom.controlsRight.forEach( function( el ) { el.addEventListener( eventName, onNavigateRightClicked, false ); } );
      dom.controlsUp.forEach( function( el ) { el.addEventListener( eventName, onNavigateUpClicked, false ); } );
      dom.controlsDown.forEach( function( el ) { el.addEventListener( eventName, onNavigateDownClicked, false ); } );
      dom.controlsPrev.forEach( function( el ) { el.addEventListener( eventName, onNavigatePrevClicked, false ); } );
      dom.controlsNext.forEach( function( el ) { el.addEventListener( eventName, onNavigateNextClicked, false ); } );
    } );

  }

  /**
   * Unbinds all event listeners.
   */
  function removeEventListeners() {

    eventsAreBound = false;

    document.removeEventListener( 'keydown', onDocumentKeyDown, false );
    document.removeEventListener( 'keypress', onDocumentKeyPress, false );
    window.removeEventListener( 'hashchange', onWindowHashChange, false );
    window.removeEventListener( 'resize', onWindowResize, false );

    dom.wrapper.removeEventListener( 'touchstart', onTouchStart, false );
    dom.wrapper.removeEventListener( 'touchmove', onTouchMove, false );
    dom.wrapper.removeEventListener( 'touchend', onTouchEnd, false );

    // IE11
    if( window.navigator.pointerEnabled ) {
      dom.wrapper.removeEventListener( 'pointerdown', onPointerDown, false );
      dom.wrapper.removeEventListener( 'pointermove', onPointerMove, false );
      dom.wrapper.removeEventListener( 'pointerup', onPointerUp, false );
    }
    // IE10
    else if( window.navigator.msPointerEnabled ) {
      dom.wrapper.removeEventListener( 'MSPointerDown', onPointerDown, false );
      dom.wrapper.removeEventListener( 'MSPointerMove', onPointerMove, false );
      dom.wrapper.removeEventListener( 'MSPointerUp', onPointerUp, false );
    }

    if ( config.progress && dom.progress ) {
      dom.progress.removeEventListener( 'click', onProgressClicked, false );
    }

    [ 'touchstart', 'click' ].forEach( function( eventName ) {
      dom.controlsLeft.forEach( function( el ) { el.removeEventListener( eventName, onNavigateLeftClicked, false ); } );
      dom.controlsRight.forEach( function( el ) { el.removeEventListener( eventName, onNavigateRightClicked, false ); } );
      dom.controlsUp.forEach( function( el ) { el.removeEventListener( eventName, onNavigateUpClicked, false ); } );
      dom.controlsDown.forEach( function( el ) { el.removeEventListener( eventName, onNavigateDownClicked, false ); } );
      dom.controlsPrev.forEach( function( el ) { el.removeEventListener( eventName, onNavigatePrevClicked, false ); } );
      dom.controlsNext.forEach( function( el ) { el.removeEventListener( eventName, onNavigateNextClicked, false ); } );
    } );

  }

  /**
   * Extend object a with the properties of object b.
   * If there's a conflict, object b takes precedence.
   */
  function extend( a, b ) {

    for( var i in b ) {
      a[ i ] = b[ i ];
    }

  }

  /**
   * Converts the target object to an array.
   */
  function toArray( o ) {

    return Array.prototype.slice.call( o );

  }

  /**
   * Utility for deserializing a value.
   */
  function deserialize( value ) {

    if( typeof value === 'string' ) {
      if( value === 'null' ) return null;
      else if( value === 'true' ) return true;
      else if( value === 'false' ) return false;
      else if( value.match( /^\d+$/ ) ) return parseFloat( value );
    }

    return value;

  }

  /**
   * Measures the distance in pixels between point a
   * and point b.
   *
   * @param {Object} a point with x/y properties
   * @param {Object} b point with x/y properties
   */
  function distanceBetween( a, b ) {

    var dx = a.x - b.x,
      dy = a.y - b.y;

    return Math.sqrt( dx*dx + dy*dy );

  }

  /**
   * Applies a CSS transform to the target element.
   */
  function transformElement( element, transform ) {

    element.style.WebkitTransform = transform;
    element.style.MozTransform = transform;
    element.style.msTransform = transform;
    element.style.transform = transform;

  }

  /**
   * Applies CSS transforms to the slides container. The container
   * is transformed from two separate sources: layout and the overview
   * mode.
   */
  function transformSlides( transforms ) {

    // Pick up new transforms from arguments
    if( typeof transforms.layout === 'string' ) slidesTransform.layout = transforms.layout;
    if( typeof transforms.overview === 'string' ) slidesTransform.overview = transforms.overview;

    // Apply the transforms to the slides container
    if( slidesTransform.layout ) {
      transformElement( dom.slides, slidesTransform.layout + ' ' + slidesTransform.overview );
    }
    else {
      transformElement( dom.slides, slidesTransform.overview );
    }

  }

  /**
   * Injects the given CSS styles into the DOM.
   */
  function injectStyleSheet( value ) {

    var tag = document.createElement( 'style' );
    tag.type = 'text/css';
    if( tag.styleSheet ) {
      tag.styleSheet.cssText = value;
    }
    else {
      tag.appendChild( document.createTextNode( value ) );
    }
    document.getElementsByTagName( 'head' )[0].appendChild( tag );

  }

  /**
   * Converts various color input formats to an {r:0,g:0,b:0} object.
   *
   * @param {String} color The string representation of a color,
   * the following formats are supported:
   * - #000
   * - #000000
   * - rgb(0,0,0)
   */
  function colorToRgb( color ) {

    var hex3 = color.match( /^#([0-9a-f]{3})$/i );
    if( hex3 && hex3[1] ) {
      hex3 = hex3[1];
      return {
        r: parseInt( hex3.charAt( 0 ), 16 ) * 0x11,
        g: parseInt( hex3.charAt( 1 ), 16 ) * 0x11,
        b: parseInt( hex3.charAt( 2 ), 16 ) * 0x11
      };
    }

    var hex6 = color.match( /^#([0-9a-f]{6})$/i );
    if( hex6 && hex6[1] ) {
      hex6 = hex6[1];
      return {
        r: parseInt( hex6.substr( 0, 2 ), 16 ),
        g: parseInt( hex6.substr( 2, 2 ), 16 ),
        b: parseInt( hex6.substr( 4, 2 ), 16 )
      };
    }

    var rgb = color.match( /^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i );
    if( rgb ) {
      return {
        r: parseInt( rgb[1], 10 ),
        g: parseInt( rgb[2], 10 ),
        b: parseInt( rgb[3], 10 )
      };
    }

    var rgba = color.match( /^rgba\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\,\s*([\d]+|[\d]*.[\d]+)\s*\)$/i );
    if( rgba ) {
      return {
        r: parseInt( rgba[1], 10 ),
        g: parseInt( rgba[2], 10 ),
        b: parseInt( rgba[3], 10 ),
        a: parseFloat( rgba[4] )
      };
    }

    return null;

  }

  /**
   * Calculates brightness on a scale of 0-255.
   *
   * @param color See colorStringToRgb for supported formats.
   */
  function colorBrightness( color ) {

    if( typeof color === 'string' ) color = colorToRgb( color );

    if( color ) {
      return ( color.r * 299 + color.g * 587 + color.b * 114 ) / 1000;
    }

    return null;

  }

  /**
   * Retrieves the height of the given element by looking
   * at the position and height of its immediate children.
   */
  function getAbsoluteHeight( element ) {

    var height = 0;

    if( element ) {
      var absoluteChildren = 0;

      toArray( element.childNodes ).forEach( function( child ) {

        if( typeof child.offsetTop === 'number' && child.style ) {
          // Count # of abs children
          if( window.getComputedStyle( child ).position === 'absolute' ) {
            absoluteChildren += 1;
          }

          height = Math.max( height, child.offsetTop + child.offsetHeight );
        }

      } );

      // If there are no absolute children, use offsetHeight
      if( absoluteChildren === 0 ) {
        height = element.offsetHeight;
      }

    }

    return height;

  }

  /**
   * Returns the remaining height within the parent of the
   * target element.
   *
   * remaining height = [ configured parent height ] - [ current parent height ]
   */
  function getRemainingHeight( element, height ) {

    height = height || 0;

    if( element ) {
      var newHeight, oldHeight = element.style.height;

      // Change the .stretch element height to 0 in order find the height of all
      // the other elements
      element.style.height = '0px';
      newHeight = height - element.parentNode.offsetHeight;

      // Restore the old height, just in case
      element.style.height = oldHeight + 'px';

      return newHeight;
    }

    return height;

  }

  /**
   * Checks if this instance is being used to print a PDF.
   */
  function isPrintingPDF() {

    return ( /print-pdf/gi ).test( window.location.search );

  }

  /**
   * Hides the address bar if we're on a mobile device.
   */
  function hideAddressBar() {

    if( config.hideAddressBar && isMobileDevice ) {
      // Events that should trigger the address bar to hide
      window.addEventListener( 'load', removeAddressBar, false );
      window.addEventListener( 'orientationchange', removeAddressBar, false );
    }

  }

  /**
   * Causes the address bar to hide on mobile devices,
   * more vertical space ftw.
   */
  function removeAddressBar() {

    setTimeout( function() {
      window.scrollTo( 0, 1 );
    }, 10 );

  }

  /**
   * Dispatches an event of the specified type from the
   * reveal DOM element.
   */
  function dispatchEvent( type, args ) {

    var event = document.createEvent( 'HTMLEvents', 1, 2 );
    event.initEvent( type, true, true );
    extend( event, args );
    dom.wrapper.dispatchEvent( event );

    // If we're in an iframe, post each reveal.js event to the
    // parent window. Used by the notes plugin
    if( config.postMessageEvents && window.parent !== window.self ) {
      window.parent.postMessage( JSON.stringify({ namespace: 'reveal', eventName: type, state: getState() }), '*' );
    }

  }

  /**
   * Wrap all links in 3D goodness.
   */
  function enableRollingLinks() {

    if( features.transforms3d && !( 'msPerspective' in document.body.style ) ) {
      var anchors = dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' a' );

      for( var i = 0, len = anchors.length; i < len; i++ ) {
        var anchor = anchors[i];

        if( anchor.textContent && !anchor.querySelector( '*' ) && ( !anchor.className || !anchor.classList.contains( anchor, 'roll' ) ) ) {
          var span = document.createElement('span');
          span.setAttribute('data-title', anchor.text);
          span.innerHTML = anchor.innerHTML;

          anchor.classList.add( 'roll' );
          anchor.innerHTML = '';
          anchor.appendChild(span);
        }
      }
    }

  }

  /**
   * Unwrap all 3D links.
   */
  function disableRollingLinks() {

    var anchors = dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' a.roll' );

    for( var i = 0, len = anchors.length; i < len; i++ ) {
      var anchor = anchors[i];
      var span = anchor.querySelector( 'span' );

      if( span ) {
        anchor.classList.remove( 'roll' );
        anchor.innerHTML = span.innerHTML;
      }
    }

  }

  /**
   * Bind preview frame links.
   */
  function enablePreviewLinks( selector ) {

    var anchors = toArray( document.querySelectorAll( selector ? selector : 'a' ) );

    anchors.forEach( function( element ) {
      if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
        element.addEventListener( 'click', onPreviewLinkClicked, false );
      }
    } );

  }

  /**
   * Unbind preview frame links.
   */
  function disablePreviewLinks() {

    var anchors = toArray( document.querySelectorAll( 'a' ) );

    anchors.forEach( function( element ) {
      if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
        element.removeEventListener( 'click', onPreviewLinkClicked, false );
      }
    } );

  }

  /**
   * Opens a preview window for the target URL.
   */
  function showPreview( url ) {

    closeOverlay();

    dom.overlay = document.createElement( 'div' );
    dom.overlay.classList.add( 'overlay' );
    dom.overlay.classList.add( 'overlay-preview' );
    dom.wrapper.appendChild( dom.overlay );

    dom.overlay.innerHTML = [
      '<header>',
        '<a class="close" href="#"><span class="icon"></span></a>',
        '<a class="external" href="'+ url +'" target="_blank"><span class="icon"></span></a>',
      '</header>',
      '<div class="spinner"></div>',
      '<div class="viewport">',
        '<iframe src="'+ url +'"></iframe>',
      '</div>'
    ].join('');

    dom.overlay.querySelector( 'iframe' ).addEventListener( 'load', function( event ) {
      dom.overlay.classList.add( 'loaded' );
    }, false );

    dom.overlay.querySelector( '.close' ).addEventListener( 'click', function( event ) {
      closeOverlay();
      event.preventDefault();
    }, false );

    dom.overlay.querySelector( '.external' ).addEventListener( 'click', function( event ) {
      closeOverlay();
    }, false );

    setTimeout( function() {
      dom.overlay.classList.add( 'visible' );
    }, 1 );

  }

  /**
   * Opens a overlay window with help material.
   */
  function showHelp() {

    if( config.help ) {

      closeOverlay();

      dom.overlay = document.createElement( 'div' );
      dom.overlay.classList.add( 'overlay' );
      dom.overlay.classList.add( 'overlay-help' );
      dom.wrapper.appendChild( dom.overlay );

      var html = '<p class="title">Keyboard Shortcuts</p><br/>';

      html += '<table><th>KEY</th><th>ACTION</th>';
      for( var key in keyboardShortcuts ) {
        html += '<tr><td>' + key + '</td><td>' + keyboardShortcuts[ key ] + '</td></tr>';
      }

      html += '</table>';

      dom.overlay.innerHTML = [
        '<header>',
          '<a class="close" href="#"><span class="icon"></span></a>',
        '</header>',
        '<div class="viewport">',
          '<div class="viewport-inner">'+ html +'</div>',
        '</div>'
      ].join('');

      dom.overlay.querySelector( '.close' ).addEventListener( 'click', function( event ) {
        closeOverlay();
        event.preventDefault();
      }, false );

      setTimeout( function() {
        dom.overlay.classList.add( 'visible' );
      }, 1 );

    }

  }

  /**
   * Closes any currently open overlay.
   */
  function closeOverlay() {

    if( dom.overlay ) {
      dom.overlay.parentNode.removeChild( dom.overlay );
      dom.overlay = null;
    }

  }

  /**
   * Applies JavaScript-controlled layout rules to the
   * presentation.
   */
  function layout() {

    if( dom.wrapper && !isPrintingPDF() ) {

      var size = getComputedSlideSize();

      var slidePadding = 20; // TODO Dig this out of DOM

      // Layout the contents of the slides
      layoutSlideContents( config.width, config.height, slidePadding );

      dom.slides.style.width = size.width + 'px';
      dom.slides.style.height = size.height + 'px';

      // Determine scale of content to fit within available space
      scale = Math.min( size.presentationWidth / size.width, size.presentationHeight / size.height );

      // Respect max/min scale settings
      scale = Math.max( scale, config.minScale );
      scale = Math.min( scale, config.maxScale );

      // Don't apply any scaling styles if scale is 1
      if( scale === 1 ) {
        dom.slides.style.zoom = '';
        dom.slides.style.left = '';
        dom.slides.style.top = '';
        dom.slides.style.bottom = '';
        dom.slides.style.right = '';
        transformSlides( { layout: '' } );
      }
      else {
        // Prefer zooming in desktop Chrome so that content remains crisp
        if( !isMobileDevice && /chrome/i.test( navigator.userAgent ) && typeof dom.slides.style.zoom !== 'undefined' ) {
          dom.slides.style.zoom = scale;
          transformSlides( { layout: '' } );
        }
        // Apply scale transform as a fallback
        else {
          dom.slides.style.left = '50%';
          dom.slides.style.top = '50%';
          dom.slides.style.bottom = 'auto';
          dom.slides.style.right = 'auto';
          transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +')' } );
        }
      }

      // Select all slides, vertical and horizontal
      var slides = toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) );

      for( var i = 0, len = slides.length; i < len; i++ ) {
        var slide = slides[ i ];

        // Don't bother updating invisible slides
        if( slide.style.display === 'none' ) {
          continue;
        }

        if( config.center || slide.classList.contains( 'center' ) ) {
          // Vertical stacks are not centred since their section
          // children will be
          if( slide.classList.contains( 'stack' ) ) {
            slide.style.top = 0;
          }
          else {
            slide.style.top = Math.max( ( ( size.height - getAbsoluteHeight( slide ) ) / 2 ) - slidePadding, 0 ) + 'px';
          }
        }
        else {
          slide.style.top = '';
        }

      }

      updateProgress();
      updateParallax();

    }

  }

  /**
   * Applies layout logic to the contents of all slides in
   * the presentation.
   */
  function layoutSlideContents( width, height, padding ) {

    // Handle sizing of elements with the 'stretch' class
    toArray( dom.slides.querySelectorAll( 'section > .stretch' ) ).forEach( function( element ) {

      // Determine how much vertical space we can use
      var remainingHeight = getRemainingHeight( element, height );

      // Consider the aspect ratio of media elements
      if( /(img|video)/gi.test( element.nodeName ) ) {
        var nw = element.naturalWidth || element.videoWidth,
          nh = element.naturalHeight || element.videoHeight;

        var es = Math.min( width / nw, remainingHeight / nh );

        element.style.width = ( nw * es ) + 'px';
        element.style.height = ( nh * es ) + 'px';

      }
      else {
        element.style.width = width + 'px';
        element.style.height = remainingHeight + 'px';
      }

    } );

  }

  /**
   * Calculates the computed pixel size of our slides. These
   * values are based on the width and height configuration
   * options.
   */
  function getComputedSlideSize( presentationWidth, presentationHeight ) {

    var size = {
      // Slide size
      width: config.width,
      height: config.height,

      // Presentation size
      presentationWidth: presentationWidth || dom.wrapper.offsetWidth,
      presentationHeight: presentationHeight || dom.wrapper.offsetHeight
    };

    // Reduce available space by margin
    size.presentationWidth -= ( size.presentationWidth * config.margin );
    size.presentationHeight -= ( size.presentationHeight * config.margin );

    // Slide width may be a percentage of available width
    if( typeof size.width === 'string' && /%$/.test( size.width ) ) {
      size.width = parseInt( size.width, 10 ) / 100 * size.presentationWidth;
    }

    // Slide height may be a percentage of available height
    if( typeof size.height === 'string' && /%$/.test( size.height ) ) {
      size.height = parseInt( size.height, 10 ) / 100 * size.presentationHeight;
    }

    return size;

  }

  /**
   * Stores the vertical index of a stack so that the same
   * vertical slide can be selected when navigating to and
   * from the stack.
   *
   * @param {HTMLElement} stack The vertical stack element
   * @param {int} v Index to memorize
   */
  function setPreviousVerticalIndex( stack, v ) {

    if( typeof stack === 'object' && typeof stack.setAttribute === 'function' ) {
      stack.setAttribute( 'data-previous-indexv', v || 0 );
    }

  }

  /**
   * Retrieves the vertical index which was stored using
   * #setPreviousVerticalIndex() or 0 if no previous index
   * exists.
   *
   * @param {HTMLElement} stack The vertical stack element
   */
  function getPreviousVerticalIndex( stack ) {

    if( typeof stack === 'object' && typeof stack.setAttribute === 'function' && stack.classList.contains( 'stack' ) ) {
      // Prefer manually defined start-indexv
      var attributeName = stack.hasAttribute( 'data-start-indexv' ) ? 'data-start-indexv' : 'data-previous-indexv';

      return parseInt( stack.getAttribute( attributeName ) || 0, 10 );
    }

    return 0;

  }

  /**
   * Displays the overview of slides (quick nav) by scaling
   * down and arranging all slide elements.
   */
  function activateOverview() {

    // Only proceed if enabled in config
    if( config.overview && !isOverview() ) {

      overview = true;

      dom.wrapper.classList.add( 'overview' );
      dom.wrapper.classList.remove( 'overview-deactivating' );

      if( features.overviewTransitions ) {
        setTimeout( function() {
          dom.wrapper.classList.add( 'overview-animated' );
        }, 1 );
      }

      // Don't auto-slide while in overview mode
      cancelAutoSlide();

      // Move the backgrounds element into the slide container to
      // that the same scaling is applied
      dom.slides.appendChild( dom.background );

      // Clicking on an overview slide navigates to it
      toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
        if( !slide.classList.contains( 'stack' ) ) {
          slide.addEventListener( 'click', onOverviewSlideClicked, true );
        }
      } );

      updateSlidesVisibility();
      layoutOverview();
      updateOverview();

      layout();

      // Notify observers of the overview showing
      dispatchEvent( 'overviewshown', {
        'indexh': indexh,
        'indexv': indexv,
        'currentSlide': currentSlide
      } );

    }

  }

  /**
   * Uses CSS transforms to position all slides in a grid for
   * display inside of the overview mode.
   */
  function layoutOverview() {

    var margin = 70;
    var slideWidth = config.width + margin,
      slideHeight = config.height + margin;

    // Reverse in RTL mode
    if( config.rtl ) {
      slideWidth = -slideWidth;
    }

    // Layout slides
    toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( hslide, h ) {
      hslide.setAttribute( 'data-index-h', h );
      transformElement( hslide, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

      if( hslide.classList.contains( 'stack' ) ) {

        toArray( hslide.querySelectorAll( 'section' ) ).forEach( function( vslide, v ) {
          vslide.setAttribute( 'data-index-h', h );
          vslide.setAttribute( 'data-index-v', v );

          transformElement( vslide, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
        } );

      }
    } );

    // Layout slide backgrounds
    toArray( dom.background.childNodes ).forEach( function( hbackground, h ) {
      transformElement( hbackground, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

      toArray( hbackground.querySelectorAll( '.slide-background' ) ).forEach( function( vbackground, v ) {
        transformElement( vbackground, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
      } );
    } );

  }

  /**
   * Moves the overview viewport to the current slides.
   * Called each time the current slide changes.
   */
  function updateOverview() {

    var margin = 70;
    var slideWidth = config.width + margin,
      slideHeight = config.height + margin;

    // Reverse in RTL mode
    if( config.rtl ) {
      slideWidth = -slideWidth;
    }

    transformSlides( {
      overview: [
        'translateX('+ ( -indexh * slideWidth ) +'px)',
        'translateY('+ ( -indexv * slideHeight ) +'px)',
        'translateZ('+ ( window.innerWidth < 400 ? -1000 : -2500 ) +'px)'
      ].join( ' ' )
    } );

  }

  /**
   * Exits the slide overview and enters the currently
   * active slide.
   */
  function deactivateOverview() {

    // Only proceed if enabled in config
    if( config.overview ) {

      overview = false;

      dom.wrapper.classList.remove( 'overview' );
      dom.wrapper.classList.remove( 'overview-animated' );

      // Temporarily add a class so that transitions can do different things
      // depending on whether they are exiting/entering overview, or just
      // moving from slide to slide
      dom.wrapper.classList.add( 'overview-deactivating' );

      setTimeout( function () {
        dom.wrapper.classList.remove( 'overview-deactivating' );
      }, 1 );

      // Move the background element back out
      dom.wrapper.appendChild( dom.background );

      // Clean up changes made to slides
      toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
        transformElement( slide, '' );

        slide.removeEventListener( 'click', onOverviewSlideClicked, true );
      } );

      // Clean up changes made to backgrounds
      toArray( dom.background.querySelectorAll( '.slide-background' ) ).forEach( function( background ) {
        transformElement( background, '' );
      } );

      transformSlides( { overview: '' } );

      slide( indexh, indexv );

      layout();

      cueAutoSlide();

      // Notify observers of the overview hiding
      dispatchEvent( 'overviewhidden', {
        'indexh': indexh,
        'indexv': indexv,
        'currentSlide': currentSlide
      } );

    }
  }

  /**
   * Toggles the slide overview mode on and off.
   *
   * @param {Boolean} override Optional flag which overrides the
   * toggle logic and forcibly sets the desired state. True means
   * overview is open, false means it's closed.
   */
  function toggleOverview( override ) {

    if( typeof override === 'boolean' ) {
      override ? activateOverview() : deactivateOverview();
    }
    else {
      isOverview() ? deactivateOverview() : activateOverview();
    }

  }

  /**
   * Checks if the overview is currently active.
   *
   * @return {Boolean} true if the overview is active,
   * false otherwise
   */
  function isOverview() {

    return overview;

  }

  /**
   * Checks if the current or specified slide is vertical
   * (nested within another slide).
   *
   * @param {HTMLElement} slide [optional] The slide to check
   * orientation of
   */
  function isVerticalSlide( slide ) {

    // Prefer slide argument, otherwise use current slide
    slide = slide ? slide : currentSlide;

    return slide && slide.parentNode && !!slide.parentNode.nodeName.match( /section/i );

  }

  /**
   * Handling the fullscreen functionality via the fullscreen API
   *
   * @see http://fullscreen.spec.whatwg.org/
   * @see https://developer.mozilla.org/en-US/docs/DOM/Using_fullscreen_mode
   */
  function enterFullscreen() {

    var element = document.body;

    // Check which implementation is available
    var requestMethod = element.requestFullScreen ||
              element.webkitRequestFullscreen ||
              element.webkitRequestFullScreen ||
              element.mozRequestFullScreen ||
              element.msRequestFullscreen;

    if( requestMethod ) {
      requestMethod.apply( element );
    }

  }

  /**
   * Enters the paused mode which fades everything on screen to
   * black.
   */
  function pause() {

    if( config.pause ) {
      var wasPaused = dom.wrapper.classList.contains( 'paused' );

      cancelAutoSlide();
      dom.wrapper.classList.add( 'paused' );

      if( wasPaused === false ) {
        dispatchEvent( 'paused' );
      }
    }

  }

  /**
   * Exits from the paused mode.
   */
  function resume() {

    var wasPaused = dom.wrapper.classList.contains( 'paused' );
    dom.wrapper.classList.remove( 'paused' );

    cueAutoSlide();

    if( wasPaused ) {
      dispatchEvent( 'resumed' );
    }

  }

  /**
   * Toggles the paused mode on and off.
   */
  function togglePause( override ) {

    if( typeof override === 'boolean' ) {
      override ? pause() : resume();
    }
    else {
      isPaused() ? resume() : pause();
    }

  }

  /**
   * Checks if we are currently in the paused mode.
   */
  function isPaused() {

    return dom.wrapper.classList.contains( 'paused' );

  }

  /**
   * Toggles the auto slide mode on and off.
   *
   * @param {Boolean} override Optional flag which sets the desired state.
   * True means autoplay starts, false means it stops.
   */

  function toggleAutoSlide( override ) {

    if( typeof override === 'boolean' ) {
      override ? resumeAutoSlide() : pauseAutoSlide();
    }

    else {
      autoSlidePaused ? resumeAutoSlide() : pauseAutoSlide();
    }

  }

  /**
   * Checks if the auto slide mode is currently on.
   */
  function isAutoSliding() {

    return !!( autoSlide && !autoSlidePaused );

  }

  /**
   * Steps from the current point in the presentation to the
   * slide which matches the specified horizontal and vertical
   * indices.
   *
   * @param {int} h Horizontal index of the target slide
   * @param {int} v Vertical index of the target slide
   * @param {int} f Optional index of a fragment within the
   * target slide to activate
   * @param {int} o Optional origin for use in multimaster environments
   */
  function slide( h, v, f, o ) {

    // Remember where we were at before
    previousSlide = currentSlide;

    // Query all horizontal slides in the deck
    var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR );

    // If no vertical index is specified and the upcoming slide is a
    // stack, resume at its previous vertical index
    if( v === undefined && !isOverview() ) {
      v = getPreviousVerticalIndex( horizontalSlides[ h ] );
    }

    // If we were on a vertical stack, remember what vertical index
    // it was on so we can resume at the same position when returning
    if( previousSlide && previousSlide.parentNode && previousSlide.parentNode.classList.contains( 'stack' ) ) {
      setPreviousVerticalIndex( previousSlide.parentNode, indexv );
    }

    // Remember the state before this slide
    var stateBefore = state.concat();

    // Reset the state array
    state.length = 0;

    var indexhBefore = indexh || 0,
      indexvBefore = indexv || 0;

    // Activate and transition to the new slide
    indexh = updateSlides( HORIZONTAL_SLIDES_SELECTOR, h === undefined ? indexh : h );
    indexv = updateSlides( VERTICAL_SLIDES_SELECTOR, v === undefined ? indexv : v );

    // Update the visibility of slides now that the indices have changed
    updateSlidesVisibility();

    layout();

    // Apply the new state
    stateLoop: for( var i = 0, len = state.length; i < len; i++ ) {
      // Check if this state existed on the previous slide. If it
      // did, we will avoid adding it repeatedly
      for( var j = 0; j < stateBefore.length; j++ ) {
        if( stateBefore[j] === state[i] ) {
          stateBefore.splice( j, 1 );
          continue stateLoop;
        }
      }

      document.documentElement.classList.add( state[i] );

      // Dispatch custom event matching the state's name
      dispatchEvent( state[i] );
    }

    // Clean up the remains of the previous state
    while( stateBefore.length ) {
      document.documentElement.classList.remove( stateBefore.pop() );
    }

    // Update the overview if it's currently active
    if( isOverview() ) {
      updateOverview();
    }

    // Find the current horizontal slide and any possible vertical slides
    // within it
    var currentHorizontalSlide = horizontalSlides[ indexh ],
      currentVerticalSlides = currentHorizontalSlide.querySelectorAll( 'section' );

    // Store references to the previous and current slides
    currentSlide = currentVerticalSlides[ indexv ] || currentHorizontalSlide;

    // Show fragment, if specified
    if( typeof f !== 'undefined' ) {
      navigateFragment( f );
    }

    // Dispatch an event if the slide changed
    var slideChanged = ( indexh !== indexhBefore || indexv !== indexvBefore );
    if( slideChanged ) {
      dispatchEvent( 'slidechanged', {
        'indexh': indexh,
        'indexv': indexv,
        'previousSlide': previousSlide,
        'currentSlide': currentSlide,
        'origin': o
      } );
    }
    else {
      // Ensure that the previous slide is never the same as the current
      previousSlide = null;
    }

    // Solves an edge case where the previous slide maintains the
    // 'present' class when navigating between adjacent vertical
    // stacks
    if( previousSlide ) {
      previousSlide.classList.remove( 'present' );
      previousSlide.setAttribute( 'aria-hidden', 'true' );

      // Reset all slides upon navigate to home
      // Issue: #285
      if ( dom.wrapper.querySelector( HOME_SLIDE_SELECTOR ).classList.contains( 'present' ) ) {
        // Launch async task
        setTimeout( function () {
          var slides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.stack') ), i;
          for( i in slides ) {
            if( slides[i] ) {
              // Reset stack
              setPreviousVerticalIndex( slides[i], 0 );
            }
          }
        }, 0 );
      }
    }

    // Handle embedded content
    if( slideChanged || !previousSlide ) {
      stopEmbeddedContent( previousSlide );
      startEmbeddedContent( currentSlide );
    }

    // Announce the current slide contents, for screen readers
    dom.statusDiv.textContent = currentSlide.textContent;

    updateControls();
    updateProgress();
    updateBackground();
    updateParallax();
    updateSlideNumber();

    // Update the URL hash
    writeURL();

    cueAutoSlide();

  }

  /**
   * Syncs the presentation with the current DOM. Useful
   * when new slides or control elements are added or when
   * the configuration has changed.
   */
  function sync() {

    // Subscribe to input
    removeEventListeners();
    addEventListeners();

    // Force a layout to make sure the current config is accounted for
    layout();

    // Reflect the current autoSlide value
    autoSlide = config.autoSlide;

    // Start auto-sliding if it's enabled
    cueAutoSlide();

    // Re-create the slide backgrounds
    createBackgrounds();

    // Write the current hash to the URL
    writeURL();

    sortAllFragments();

    updateControls();
    updateProgress();
    updateBackground( true );
    updateSlideNumber();
    updateSlidesVisibility();

    formatEmbeddedContent();
    startEmbeddedContent( currentSlide );

    if( isOverview() ) {
      layoutOverview();
    }

  }

  /**
   * Resets all vertical slides so that only the first
   * is visible.
   */
  function resetVerticalSlides() {

    var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );
    horizontalSlides.forEach( function( horizontalSlide ) {

      var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );
      verticalSlides.forEach( function( verticalSlide, y ) {

        if( y > 0 ) {
          verticalSlide.classList.remove( 'present' );
          verticalSlide.classList.remove( 'past' );
          verticalSlide.classList.add( 'future' );
          verticalSlide.setAttribute( 'aria-hidden', 'true' );
        }

      } );

    } );

  }

  /**
   * Sorts and formats all of fragments in the
   * presentation.
   */
  function sortAllFragments() {

    var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );
    horizontalSlides.forEach( function( horizontalSlide ) {

      var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );
      verticalSlides.forEach( function( verticalSlide, y ) {

        sortFragments( verticalSlide.querySelectorAll( '.fragment' ) );

      } );

      if( verticalSlides.length === 0 ) sortFragments( horizontalSlide.querySelectorAll( '.fragment' ) );

    } );

  }

  /**
   * Updates one dimension of slides by showing the slide
   * with the specified index.
   *
   * @param {String} selector A CSS selector that will fetch
   * the group of slides we are working with
   * @param {Number} index The index of the slide that should be
   * shown
   *
   * @return {Number} The index of the slide that is now shown,
   * might differ from the passed in index if it was out of
   * bounds.
   */
  function updateSlides( selector, index ) {

    // Select all slides and convert the NodeList result to
    // an array
    var slides = toArray( dom.wrapper.querySelectorAll( selector ) ),
      slidesLength = slides.length;

    var printMode = isPrintingPDF();

    if( slidesLength ) {

      // Should the index loop?
      if( config.loop ) {
        index %= slidesLength;

        if( index < 0 ) {
          index = slidesLength + index;
        }
      }

      // Enforce max and minimum index bounds
      index = Math.max( Math.min( index, slidesLength - 1 ), 0 );

      for( var i = 0; i < slidesLength; i++ ) {
        var element = slides[i];

        var reverse = config.rtl && !isVerticalSlide( element );

        element.classList.remove( 'past' );
        element.classList.remove( 'present' );
        element.classList.remove( 'future' );

        // http://www.w3.org/html/wg/drafts/html/master/editing.html#the-hidden-attribute
        element.setAttribute( 'hidden', '' );
        element.setAttribute( 'aria-hidden', 'true' );

        // If this element contains vertical slides
        if( element.querySelector( 'section' ) ) {
          element.classList.add( 'stack' );
        }

        // If we're printing static slides, all slides are "present"
        if( printMode ) {
          element.classList.add( 'present' );
          continue;
        }

        if( i < index ) {
          // Any element previous to index is given the 'past' class
          element.classList.add( reverse ? 'future' : 'past' );

          if( config.fragments ) {
            var pastFragments = toArray( element.querySelectorAll( '.fragment' ) );

            // Show all fragments on prior slides
            while( pastFragments.length ) {
              var pastFragment = pastFragments.pop();
              pastFragment.classList.add( 'visible' );
              pastFragment.classList.remove( 'current-fragment' );
            }
          }
        }
        else if( i > index ) {
          // Any element subsequent to index is given the 'future' class
          element.classList.add( reverse ? 'past' : 'future' );

          if( config.fragments ) {
            var futureFragments = toArray( element.querySelectorAll( '.fragment.visible' ) );

            // No fragments in future slides should be visible ahead of time
            while( futureFragments.length ) {
              var futureFragment = futureFragments.pop();
              futureFragment.classList.remove( 'visible' );
              futureFragment.classList.remove( 'current-fragment' );
            }
          }
        }
      }

      // Mark the current slide as present
      slides[index].classList.add( 'present' );
      slides[index].removeAttribute( 'hidden' );
      slides[index].removeAttribute( 'aria-hidden' );

      // If this slide has a state associated with it, add it
      // onto the current state of the deck
      var slideState = slides[index].getAttribute( 'data-state' );
      if( slideState ) {
        state = state.concat( slideState.split( ' ' ) );
      }

    }
    else {
      // Since there are no slides we can't be anywhere beyond the
      // zeroth index
      index = 0;
    }

    return index;

  }

  /**
   * Optimization method; hide all slides that are far away
   * from the present slide.
   */
  function updateSlidesVisibility() {

    // Select all slides and convert the NodeList result to
    // an array
    var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ),
      horizontalSlidesLength = horizontalSlides.length,
      distanceX,
      distanceY;

    if( horizontalSlidesLength && typeof indexh !== 'undefined' ) {

      // The number of steps away from the present slide that will
      // be visible
      var viewDistance = isOverview() ? 10 : config.viewDistance;

      // Limit view distance on weaker devices
      if( isMobileDevice ) {
        viewDistance = isOverview() ? 6 : 2;
      }

      // All slides need to be visible when exporting to PDF
      if( isPrintingPDF() ) {
        viewDistance = Number.MAX_VALUE;
      }

      for( var x = 0; x < horizontalSlidesLength; x++ ) {
        var horizontalSlide = horizontalSlides[x];

        var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) ),
          verticalSlidesLength = verticalSlides.length;

        // Determine how far away this slide is from the present
        distanceX = Math.abs( ( indexh || 0 ) - x ) || 0;

        // If the presentation is looped, distance should measure
        // 1 between the first and last slides
        if( config.loop ) {
          distanceX = Math.abs( ( ( indexh || 0 ) - x ) % ( horizontalSlidesLength - viewDistance ) ) || 0;
        }

        // Show the horizontal slide if it's within the view distance
        if( distanceX < viewDistance ) {
          showSlide( horizontalSlide );
        }
        else {
          hideSlide( horizontalSlide );
        }

        if( verticalSlidesLength ) {

          var oy = getPreviousVerticalIndex( horizontalSlide );

          for( var y = 0; y < verticalSlidesLength; y++ ) {
            var verticalSlide = verticalSlides[y];

            distanceY = x === ( indexh || 0 ) ? Math.abs( ( indexv || 0 ) - y ) : Math.abs( y - oy );

            if( distanceX + distanceY < viewDistance ) {
              showSlide( verticalSlide );
            }
            else {
              hideSlide( verticalSlide );
            }
          }

        }
      }

    }

  }

  /**
   * Updates the progress bar to reflect the current slide.
   */
  function updateProgress() {

    // Update progress if enabled
    if( config.progress && dom.progressbar ) {

      dom.progressbar.style.width = getProgress() * dom.wrapper.offsetWidth + 'px';

    }

  }

  /**
   * Updates the slide number div to reflect the current slide.
   *
   * Slide number format can be defined as a string using the
   * following variables:
   *  h: current slide's horizontal index
   *  v: current slide's vertical index
   *  c: current slide index (flattened)
   *  t: total number of slides (flattened)
   */
  function updateSlideNumber() {

    // Update slide number if enabled
    if( config.slideNumber && dom.slideNumber) {

      // Default to only showing the current slide number
      var format = 'c';

      // Check if a custom slide number format is available
      if( typeof config.slideNumber === 'string' ) {
        format = config.slideNumber;
      }

      dom.slideNumber.innerHTML = format.replace( /h/g, indexh )
                        .replace( /v/g, indexv )
                        .replace( /c/g, getSlidePastCount() + 1 )
                        .replace( /t/g, getTotalSlides() );
    }

  }

  /**
   * Updates the state of all control/navigation arrows.
   */
  function updateControls() {

    var routes = availableRoutes();
    var fragments = availableFragments();

    // Remove the 'enabled' class from all directions
    dom.controlsLeft.concat( dom.controlsRight )
            .concat( dom.controlsUp )
            .concat( dom.controlsDown )
            .concat( dom.controlsPrev )
            .concat( dom.controlsNext ).forEach( function( node ) {
      node.classList.remove( 'enabled' );
      node.classList.remove( 'fragmented' );
    } );

    // Add the 'enabled' class to the available routes
    if( routes.left ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'enabled' ); } );
    if( routes.right ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'enabled' ); } );
    if( routes.up ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'enabled' ); } );
    if( routes.down ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'enabled' ); } );

    // Prev/next buttons
    if( routes.left || routes.up ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'enabled' ); } );
    if( routes.right || routes.down ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'enabled' ); } );

    // Highlight fragment directions
    if( currentSlide ) {

      // Always apply fragment decorator to prev/next buttons
      if( fragments.prev ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
      if( fragments.next ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );

      // Apply fragment decorators to directional buttons based on
      // what slide axis they are in
      if( isVerticalSlide( currentSlide ) ) {
        if( fragments.prev ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
        if( fragments.next ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
      }
      else {
        if( fragments.prev ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
        if( fragments.next ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
      }

    }

  }

  /**
   * Updates the background elements to reflect the current
   * slide.
   *
   * @param {Boolean} includeAll If true, the backgrounds of
   * all vertical slides (not just the present) will be updated.
   */
  function updateBackground( includeAll ) {

    var currentBackground = null;

    // Reverse past/future classes when in RTL mode
    var horizontalPast = config.rtl ? 'future' : 'past',
      horizontalFuture = config.rtl ? 'past' : 'future';

    // Update the classes of all backgrounds to match the
    // states of their slides (past/present/future)
    toArray( dom.background.childNodes ).forEach( function( backgroundh, h ) {

      backgroundh.classList.remove( 'past' );
      backgroundh.classList.remove( 'present' );
      backgroundh.classList.remove( 'future' );

      if( h < indexh ) {
        backgroundh.classList.add( horizontalPast );
      }
      else if ( h > indexh ) {
        backgroundh.classList.add( horizontalFuture );
      }
      else {
        backgroundh.classList.add( 'present' );

        // Store a reference to the current background element
        currentBackground = backgroundh;
      }

      if( includeAll || h === indexh ) {
        toArray( backgroundh.querySelectorAll( '.slide-background' ) ).forEach( function( backgroundv, v ) {

          backgroundv.classList.remove( 'past' );
          backgroundv.classList.remove( 'present' );
          backgroundv.classList.remove( 'future' );

          if( v < indexv ) {
            backgroundv.classList.add( 'past' );
          }
          else if ( v > indexv ) {
            backgroundv.classList.add( 'future' );
          }
          else {
            backgroundv.classList.add( 'present' );

            // Only if this is the present horizontal and vertical slide
            if( h === indexh ) currentBackground = backgroundv;
          }

        } );
      }

    } );

    // Stop any currently playing video background
    if( previousBackground ) {

      var previousVideo = previousBackground.querySelector( 'video' );
      if( previousVideo ) previousVideo.pause();

    }

    if( currentBackground ) {

      // Start video playback
      var currentVideo = currentBackground.querySelector( 'video' );
      if( currentVideo ) {
        currentVideo.currentTime = 0;
        currentVideo.play();
      }

      var backgroundImageURL = currentBackground.style.backgroundImage || '';

      // Restart GIFs (doesn't work in Firefox)
      if( /\.gif/i.test( backgroundImageURL ) ) {
        currentBackground.style.backgroundImage = '';
        window.getComputedStyle( currentBackground ).opacity;
        currentBackground.style.backgroundImage = backgroundImageURL;
      }

      // Don't transition between identical backgrounds. This
      // prevents unwanted flicker.
      var previousBackgroundHash = previousBackground ? previousBackground.getAttribute( 'data-background-hash' ) : null;
      var currentBackgroundHash = currentBackground.getAttribute( 'data-background-hash' );
      if( currentBackgroundHash && currentBackgroundHash === previousBackgroundHash && currentBackground !== previousBackground ) {
        dom.background.classList.add( 'no-transition' );
      }

      previousBackground = currentBackground;

    }

    // If there's a background brightness flag for this slide,
    // bubble it to the .reveal container
    if( currentSlide ) {
      [ 'has-light-background', 'has-dark-background' ].forEach( function( classToBubble ) {
        if( currentSlide.classList.contains( classToBubble ) ) {
          dom.wrapper.classList.add( classToBubble );
        }
        else {
          dom.wrapper.classList.remove( classToBubble );
        }
      } );
    }

    // Allow the first background to apply without transition
    setTimeout( function() {
      dom.background.classList.remove( 'no-transition' );
    }, 1 );

  }

  /**
   * Updates the position of the parallax background based
   * on the current slide index.
   */
  function updateParallax() {

    if( config.parallaxBackgroundImage ) {

      var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
        verticalSlides = dom.wrapper.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

      var backgroundSize = dom.background.style.backgroundSize.split( ' ' ),
        backgroundWidth, backgroundHeight;

      if( backgroundSize.length === 1 ) {
        backgroundWidth = backgroundHeight = parseInt( backgroundSize[0], 10 );
      }
      else {
        backgroundWidth = parseInt( backgroundSize[0], 10 );
        backgroundHeight = parseInt( backgroundSize[1], 10 );
      }

      var slideWidth = dom.background.offsetWidth,
        horizontalSlideCount = horizontalSlides.length,
        horizontalOffsetMultiplier,
        horizontalOffset;

      if( typeof config.parallaxBackgroundHorizontal === 'number' ) {
        horizontalOffsetMultiplier = config.parallaxBackgroundHorizontal;
      }
      else {
        horizontalOffsetMultiplier = ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 );
      }

      horizontalOffset = horizontalOffsetMultiplier * indexh * -1;

      var slideHeight = dom.background.offsetHeight,
        verticalSlideCount = verticalSlides.length,
        verticalOffsetMultiplier,
        verticalOffset;

      if( typeof config.parallaxBackgroundVertical === 'number' ) {
        verticalOffsetMultiplier = config.parallaxBackgroundVertical;
      }
      else {
        verticalOffsetMultiplier = ( backgroundHeight - slideHeight ) / ( verticalSlideCount-1 );
      }

      verticalOffset = verticalSlideCount > 0 ?  verticalOffsetMultiplier * indexv * 1 : 0;

      dom.background.style.backgroundPosition = horizontalOffset + 'px ' + -verticalOffset + 'px';

    }

  }

  /**
   * Called when the given slide is within the configured view
   * distance. Shows the slide element and loads any content
   * that is set to load lazily (data-src).
   */
  function showSlide( slide ) {

    // Show the slide element
    slide.style.display = 'block';

    // Media elements with data-src attributes
    toArray( slide.querySelectorAll( 'img[data-src], video[data-src], audio[data-src]' ) ).forEach( function( element ) {
      element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
      element.removeAttribute( 'data-src' );
    } );

    // Media elements with <source> children
    toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( media ) {
      var sources = 0;

      toArray( media.querySelectorAll( 'source[data-src]' ) ).forEach( function( source ) {
        source.setAttribute( 'src', source.getAttribute( 'data-src' ) );
        source.removeAttribute( 'data-src' );
        sources += 1;
      } );

      // If we rewrote sources for this video/audio element, we need
      // to manually tell it to load from its new origin
      if( sources > 0 ) {
        media.load();
      }
    } );


    // Show the corresponding background element
    var indices = getIndices( slide );
    var background = getSlideBackground( indices.h, indices.v );
    if( background ) {
      background.style.display = 'block';

      // If the background contains media, load it
      if( background.hasAttribute( 'data-loaded' ) === false ) {
        background.setAttribute( 'data-loaded', 'true' );

        var backgroundImage = slide.getAttribute( 'data-background-image' ),
          backgroundVideo = slide.getAttribute( 'data-background-video' ),
          backgroundVideoLoop = slide.hasAttribute( 'data-background-video-loop' ),
          backgroundIframe = slide.getAttribute( 'data-background-iframe' );

        // Images
        if( backgroundImage ) {
          background.style.backgroundImage = 'url('+ backgroundImage +')';
        }
        // Videos
        else if ( backgroundVideo && !isSpeakerNotes() ) {
          var video = document.createElement( 'video' );

          if( backgroundVideoLoop ) {
            video.setAttribute( 'loop', '' );
          }

          // Support comma separated lists of video sources
          backgroundVideo.split( ',' ).forEach( function( source ) {
            video.innerHTML += '<source src="'+ source +'">';
          } );

          background.appendChild( video );
        }
        // Iframes
        else if( backgroundIframe ) {
          var iframe = document.createElement( 'iframe' );
            iframe.setAttribute( 'src', backgroundIframe );
            iframe.style.width  = '100%';
            iframe.style.height = '100%';
            iframe.style.maxHeight = '100%';
            iframe.style.maxWidth = '100%';

          background.appendChild( iframe );
        }
      }
    }

  }

  /**
   * Called when the given slide is moved outside of the
   * configured view distance.
   */
  function hideSlide( slide ) {

    // Hide the slide element
    slide.style.display = 'none';

    // Hide the corresponding background element
    var indices = getIndices( slide );
    var background = getSlideBackground( indices.h, indices.v );
    if( background ) {
      background.style.display = 'none';
    }

  }

  /**
   * Determine what available routes there are for navigation.
   *
   * @return {Object} containing four booleans: left/right/up/down
   */
  function availableRoutes() {

    var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
      verticalSlides = dom.wrapper.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

    var routes = {
      left: indexh > 0 || config.loop,
      right: indexh < horizontalSlides.length - 1 || config.loop,
      up: indexv > 0,
      down: indexv < verticalSlides.length - 1
    };

    // reverse horizontal controls for rtl
    if( config.rtl ) {
      var left = routes.left;
      routes.left = routes.right;
      routes.right = left;
    }

    return routes;

  }

  /**
   * Returns an object describing the available fragment
   * directions.
   *
   * @return {Object} two boolean properties: prev/next
   */
  function availableFragments() {

    if( currentSlide && config.fragments ) {
      var fragments = currentSlide.querySelectorAll( '.fragment' );
      var hiddenFragments = currentSlide.querySelectorAll( '.fragment:not(.visible)' );

      return {
        prev: fragments.length - hiddenFragments.length > 0,
        next: !!hiddenFragments.length
      };
    }
    else {
      return { prev: false, next: false };
    }

  }

  /**
   * Enforces origin-specific format rules for embedded media.
   */
  function formatEmbeddedContent() {

    var _appendParamToIframeSource = function( sourceAttribute, sourceURL, param ) {
      toArray( dom.slides.querySelectorAll( 'iframe['+ sourceAttribute +'*="'+ sourceURL +'"]' ) ).forEach( function( el ) {
        var src = el.getAttribute( sourceAttribute );
        if( src && src.indexOf( param ) === -1 ) {
          el.setAttribute( sourceAttribute, src + ( !/\?/.test( src ) ? '?' : '&' ) + param );
        }
      });
    };

    // YouTube frames must include "?enablejsapi=1"
    _appendParamToIframeSource( 'src', 'youtube.com/embed/', 'enablejsapi=1' );
    _appendParamToIframeSource( 'data-src', 'youtube.com/embed/', 'enablejsapi=1' );

    // Vimeo frames must include "?api=1"
    _appendParamToIframeSource( 'src', 'player.vimeo.com/', 'api=1' );
    _appendParamToIframeSource( 'data-src', 'player.vimeo.com/', 'api=1' );

  }

  /**
   * Start playback of any embedded content inside of
   * the targeted slide.
   */
  function startEmbeddedContent( slide ) {

    if( slide && !isSpeakerNotes() ) {
      // Restart GIFs
      toArray( slide.querySelectorAll( 'img[src$=".gif"]' ) ).forEach( function( el ) {
        // Setting the same unchanged source like this was confirmed
        // to work in Chrome, FF & Safari
        el.setAttribute( 'src', el.getAttribute( 'src' ) );
      } );

      // HTML5 media elements
      toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
        if( el.hasAttribute( 'data-autoplay' ) && typeof el.play === 'function' ) {
          el.play();
        }
      } );

      // Normal iframes
      toArray( slide.querySelectorAll( 'iframe[src]' ) ).forEach( function( el ) {
        startEmbeddedIframe( { target: el } );
      } );

      // Lazy loading iframes
      toArray( slide.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
        if( el.getAttribute( 'src' ) !== el.getAttribute( 'data-src' ) ) {
          el.removeEventListener( 'load', startEmbeddedIframe ); // remove first to avoid dupes
          el.addEventListener( 'load', startEmbeddedIframe );
          el.setAttribute( 'src', el.getAttribute( 'data-src' ) );
        }
      } );
    }

  }

  /**
   * "Starts" the content of an embedded iframe using the
   * postmessage API.
   */
  function startEmbeddedIframe( event ) {

    var iframe = event.target;

    // YouTube postMessage API
    if( /youtube\.com\/embed\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
      iframe.contentWindow.postMessage( '{"event":"command","func":"playVideo","args":""}', '*' );
    }
    // Vimeo postMessage API
    else if( /player\.vimeo\.com\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
      iframe.contentWindow.postMessage( '{"method":"play"}', '*' );
    }
    // Generic postMessage API
    else {
      iframe.contentWindow.postMessage( 'slide:start', '*' );
    }

  }

  /**
   * Stop playback of any embedded content inside of
   * the targeted slide.
   */
  function stopEmbeddedContent( slide ) {

    if( slide && slide.parentNode ) {
      // HTML5 media elements
      toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
        if( !el.hasAttribute( 'data-ignore' ) && typeof el.pause === 'function' ) {
          el.pause();
        }
      } );

      // Generic postMessage API for non-lazy loaded iframes
      toArray( slide.querySelectorAll( 'iframe' ) ).forEach( function( el ) {
        el.contentWindow.postMessage( 'slide:stop', '*' );
        el.removeEventListener( 'load', startEmbeddedIframe );
      });

      // YouTube postMessage API
      toArray( slide.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( function( el ) {
        if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
          el.contentWindow.postMessage( '{"event":"command","func":"pauseVideo","args":""}', '*' );
        }
      });

      // Vimeo postMessage API
      toArray( slide.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( function( el ) {
        if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
          el.contentWindow.postMessage( '{"method":"pause"}', '*' );
        }
      });

      // Lazy loading iframes
      toArray( slide.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
        // Only removing the src doesn't actually unload the frame
        // in all browsers (Firefox) so we set it to blank first
        el.setAttribute( 'src', 'about:blank' );
        el.removeAttribute( 'src' );
      } );
    }

  }

  /**
   * Returns the number of past slides. This can be used as a global
   * flattened index for slides.
   */
  function getSlidePastCount() {

    var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

    // The number of past slides
    var pastCount = 0;

    // Step through all slides and count the past ones
    mainLoop: for( var i = 0; i < horizontalSlides.length; i++ ) {

      var horizontalSlide = horizontalSlides[i];
      var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );

      for( var j = 0; j < verticalSlides.length; j++ ) {

        // Stop as soon as we arrive at the present
        if( verticalSlides[j].classList.contains( 'present' ) ) {
          break mainLoop;
        }

        pastCount++;

      }

      // Stop as soon as we arrive at the present
      if( horizontalSlide.classList.contains( 'present' ) ) {
        break;
      }

      // Don't count the wrapping section for vertical slides
      if( horizontalSlide.classList.contains( 'stack' ) === false ) {
        pastCount++;
      }

    }

    return pastCount;

  }

  /**
   * Returns a value ranging from 0-1 that represents
   * how far into the presentation we have navigated.
   */
  function getProgress() {

    // The number of past and total slides
    var totalCount = getTotalSlides();
    var pastCount = getSlidePastCount();

    if( currentSlide ) {

      var allFragments = currentSlide.querySelectorAll( '.fragment' );

      // If there are fragments in the current slide those should be
      // accounted for in the progress.
      if( allFragments.length > 0 ) {
        var visibleFragments = currentSlide.querySelectorAll( '.fragment.visible' );

        // This value represents how big a portion of the slide progress
        // that is made up by its fragments (0-1)
        var fragmentWeight = 0.9;

        // Add fragment progress to the past slide count
        pastCount += ( visibleFragments.length / allFragments.length ) * fragmentWeight;
      }

    }

    return pastCount / ( totalCount - 1 );

  }

  /**
   * Checks if this presentation is running inside of the
   * speaker notes window.
   */
  function isSpeakerNotes() {

    return !!window.location.search.match( /receiver/gi );

  }

  /**
   * Reads the current URL (hash) and navigates accordingly.
   */
  function readURL() {

    var hash = window.location.hash;

    // Attempt to parse the hash as either an index or name
    var bits = hash.slice( 2 ).split( '/' ),
      name = hash.replace( /#|\//gi, '' );

    // If the first bit is invalid and there is a name we can
    // assume that this is a named link
    if( isNaN( parseInt( bits[0], 10 ) ) && name.length ) {
      var element;

      // Ensure the named link is a valid HTML ID attribute
      if( /^[a-zA-Z][\w:.-]*$/.test( name ) ) {
        // Find the slide with the specified ID
        element = document.getElementById( name );
      }

      if( element ) {
        // Find the position of the named slide and navigate to it
        var indices = Reveal.getIndices( element );
        slide( indices.h, indices.v );
      }
      // If the slide doesn't exist, navigate to the current slide
      else {
        slide( indexh || 0, indexv || 0 );
      }
    }
    else {
      // Read the index components of the hash
      var h = parseInt( bits[0], 10 ) || 0,
        v = parseInt( bits[1], 10 ) || 0;

      if( h !== indexh || v !== indexv ) {
        slide( h, v );
      }
    }

  }

  /**
   * Updates the page URL (hash) to reflect the current
   * state.
   *
   * @param {Number} delay The time in ms to wait before
   * writing the hash
   */
  function writeURL( delay ) {

    if( config.history ) {

      // Make sure there's never more than one timeout running
      clearTimeout( writeURLTimeout );

      // If a delay is specified, timeout this call
      if( typeof delay === 'number' ) {
        writeURLTimeout = setTimeout( writeURL, delay );
      }
      else if( currentSlide ) {
        var url = '/';

        // Attempt to create a named link based on the slide's ID
        var id = currentSlide.getAttribute( 'id' );
        if( id ) {
          id = id.toLowerCase();
          id = id.replace( /[^a-zA-Z0-9\-\_\:\.]/g, '' );
        }

        // If the current slide has an ID, use that as a named link
        if( typeof id === 'string' && id.length ) {
          url = '/' + id;
        }
        // Otherwise use the /h/v index
        else {
          if( indexh > 0 || indexv > 0 ) url += indexh;
          if( indexv > 0 ) url += '/' + indexv;
        }

        window.location.hash = url;
      }
    }

  }

  /**
   * Retrieves the h/v location of the current, or specified,
   * slide.
   *
   * @param {HTMLElement} slide If specified, the returned
   * index will be for this slide rather than the currently
   * active one
   *
   * @return {Object} { h: <int>, v: <int>, f: <int> }
   */
  function getIndices( slide ) {

    // By default, return the current indices
    var h = indexh,
      v = indexv,
      f;

    // If a slide is specified, return the indices of that slide
    if( slide ) {
      var isVertical = isVerticalSlide( slide );
      var slideh = isVertical ? slide.parentNode : slide;

      // Select all horizontal slides
      var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

      // Now that we know which the horizontal slide is, get its index
      h = Math.max( horizontalSlides.indexOf( slideh ), 0 );

      // Assume we're not vertical
      v = undefined;

      // If this is a vertical slide, grab the vertical index
      if( isVertical ) {
        v = Math.max( toArray( slide.parentNode.querySelectorAll( 'section' ) ).indexOf( slide ), 0 );
      }
    }

    if( !slide && currentSlide ) {
      var hasFragments = currentSlide.querySelectorAll( '.fragment' ).length > 0;
      if( hasFragments ) {
        var currentFragment = currentSlide.querySelector( '.current-fragment' );
        if( currentFragment && currentFragment.hasAttribute( 'data-fragment-index' ) ) {
          f = parseInt( currentFragment.getAttribute( 'data-fragment-index' ), 10 );
        }
        else {
          f = currentSlide.querySelectorAll( '.fragment.visible' ).length - 1;
        }
      }
    }

    return { h: h, v: v, f: f };

  }

  /**
   * Retrieves the total number of slides in this presentation.
   */
  function getTotalSlides() {

    return dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ':not(.stack)' ).length;

  }

  /**
   * Returns the slide element matching the specified index.
   */
  function getSlide( x, y ) {

    var horizontalSlide = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR )[ x ];
    var verticalSlides = horizontalSlide && horizontalSlide.querySelectorAll( 'section' );

    if( verticalSlides && verticalSlides.length && typeof y === 'number' ) {
      return verticalSlides ? verticalSlides[ y ] : undefined;
    }

    return horizontalSlide;

  }

  /**
   * Returns the background element for the given slide.
   * All slides, even the ones with no background properties
   * defined, have a background element so as long as the
   * index is valid an element will be returned.
   */
  function getSlideBackground( x, y ) {

    // When printing to PDF the slide backgrounds are nested
    // inside of the slides
    if( isPrintingPDF() ) {
      var slide = getSlide( x, y );
      if( slide ) {
        var background = slide.querySelector( '.slide-background' );
        if( background && background.parentNode === slide ) {
          return background;
        }
      }

      return undefined;
    }

    var horizontalBackground = dom.wrapper.querySelectorAll( '.backgrounds>.slide-background' )[ x ];
    var verticalBackgrounds = horizontalBackground && horizontalBackground.querySelectorAll( '.slide-background' );

    if( verticalBackgrounds && verticalBackgrounds.length && typeof y === 'number' ) {
      return verticalBackgrounds ? verticalBackgrounds[ y ] : undefined;
    }

    return horizontalBackground;

  }

  /**
   * Retrieves the current state of the presentation as
   * an object. This state can then be restored at any
   * time.
   */
  function getState() {

    var indices = getIndices();

    return {
      indexh: indices.h,
      indexv: indices.v,
      indexf: indices.f,
      paused: isPaused(),
      overview: isOverview()
    };

  }

  /**
   * Restores the presentation to the given state.
   *
   * @param {Object} state As generated by getState()
   */
  function setState( state ) {

    if( typeof state === 'object' ) {
      slide( deserialize( state.indexh ), deserialize( state.indexv ), deserialize( state.indexf ) );

      var pausedFlag = deserialize( state.paused ),
        overviewFlag = deserialize( state.overview );

      if( typeof pausedFlag === 'boolean' && pausedFlag !== isPaused() ) {
        togglePause( pausedFlag );
      }

      if( typeof overviewFlag === 'boolean' && overviewFlag !== isOverview() ) {
        toggleOverview( overviewFlag );
      }
    }

  }

  /**
   * Return a sorted fragments list, ordered by an increasing
   * "data-fragment-index" attribute.
   *
   * Fragments will be revealed in the order that they are returned by
   * this function, so you can use the index attributes to control the
   * order of fragment appearance.
   *
   * To maintain a sensible default fragment order, fragments are presumed
   * to be passed in document order. This function adds a "fragment-index"
   * attribute to each node if such an attribute is not already present,
   * and sets that attribute to an integer value which is the position of
   * the fragment within the fragments list.
   */
  function sortFragments( fragments ) {

    fragments = toArray( fragments );

    var ordered = [],
      unordered = [],
      sorted = [];

    // Group ordered and unordered elements
    fragments.forEach( function( fragment, i ) {
      if( fragment.hasAttribute( 'data-fragment-index' ) ) {
        var index = parseInt( fragment.getAttribute( 'data-fragment-index' ), 10 );

        if( !ordered[index] ) {
          ordered[index] = [];
        }

        ordered[index].push( fragment );
      }
      else {
        unordered.push( [ fragment ] );
      }
    } );

    // Append fragments without explicit indices in their
    // DOM order
    ordered = ordered.concat( unordered );

    // Manually count the index up per group to ensure there
    // are no gaps
    var index = 0;

    // Push all fragments in their sorted order to an array,
    // this flattens the groups
    ordered.forEach( function( group ) {
      group.forEach( function( fragment ) {
        sorted.push( fragment );
        fragment.setAttribute( 'data-fragment-index', index );
      } );

      index ++;
    } );

    return sorted;

  }

  /**
   * Navigate to the specified slide fragment.
   *
   * @param {Number} index The index of the fragment that
   * should be shown, -1 means all are invisible
   * @param {Number} offset Integer offset to apply to the
   * fragment index
   *
   * @return {Boolean} true if a change was made in any
   * fragments visibility as part of this call
   */
  function navigateFragment( index, offset ) {

    if( currentSlide && config.fragments ) {

      var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment' ) );
      if( fragments.length ) {

        // If no index is specified, find the current
        if( typeof index !== 'number' ) {
          var lastVisibleFragment = sortFragments( currentSlide.querySelectorAll( '.fragment.visible' ) ).pop();

          if( lastVisibleFragment ) {
            index = parseInt( lastVisibleFragment.getAttribute( 'data-fragment-index' ) || 0, 10 );
          }
          else {
            index = -1;
          }
        }

        // If an offset is specified, apply it to the index
        if( typeof offset === 'number' ) {
          index += offset;
        }

        var fragmentsShown = [],
          fragmentsHidden = [];

        toArray( fragments ).forEach( function( element, i ) {

          if( element.hasAttribute( 'data-fragment-index' ) ) {
            i = parseInt( element.getAttribute( 'data-fragment-index' ), 10 );
          }

          // Visible fragments
          if( i <= index ) {
            if( !element.classList.contains( 'visible' ) ) fragmentsShown.push( element );
            element.classList.add( 'visible' );
            element.classList.remove( 'current-fragment' );

            // Announce the fragments one by one to the Screen Reader
            dom.statusDiv.textContent = element.textContent;

            if( i === index ) {
              element.classList.add( 'current-fragment' );
            }
          }
          // Hidden fragments
          else {
            if( element.classList.contains( 'visible' ) ) fragmentsHidden.push( element );
            element.classList.remove( 'visible' );
            element.classList.remove( 'current-fragment' );
          }


        } );

        if( fragmentsHidden.length ) {
          dispatchEvent( 'fragmenthidden', { fragment: fragmentsHidden[0], fragments: fragmentsHidden } );
        }

        if( fragmentsShown.length ) {
          dispatchEvent( 'fragmentshown', { fragment: fragmentsShown[0], fragments: fragmentsShown } );
        }

        updateControls();
        updateProgress();

        return !!( fragmentsShown.length || fragmentsHidden.length );

      }

    }

    return false;

  }

  /**
   * Navigate to the next slide fragment.
   *
   * @return {Boolean} true if there was a next fragment,
   * false otherwise
   */
  function nextFragment() {

    return navigateFragment( null, 1 );

  }

  /**
   * Navigate to the previous slide fragment.
   *
   * @return {Boolean} true if there was a previous fragment,
   * false otherwise
   */
  function previousFragment() {

    return navigateFragment( null, -1 );

  }

  /**
   * Cues a new automated slide if enabled in the config.
   */
  function cueAutoSlide() {

    cancelAutoSlide();

    if( currentSlide ) {

      var currentFragment = currentSlide.querySelector( '.current-fragment' );

      var fragmentAutoSlide = currentFragment ? currentFragment.getAttribute( 'data-autoslide' ) : null;
      var parentAutoSlide = currentSlide.parentNode ? currentSlide.parentNode.getAttribute( 'data-autoslide' ) : null;
      var slideAutoSlide = currentSlide.getAttribute( 'data-autoslide' );

      // Pick value in the following priority order:
      // 1. Current fragment's data-autoslide
      // 2. Current slide's data-autoslide
      // 3. Parent slide's data-autoslide
      // 4. Global autoSlide setting
      if( fragmentAutoSlide ) {
        autoSlide = parseInt( fragmentAutoSlide, 10 );
      }
      else if( slideAutoSlide ) {
        autoSlide = parseInt( slideAutoSlide, 10 );
      }
      else if( parentAutoSlide ) {
        autoSlide = parseInt( parentAutoSlide, 10 );
      }
      else {
        autoSlide = config.autoSlide;
      }

      // If there are media elements with data-autoplay,
      // automatically set the autoSlide duration to the
      // length of that media. Not applicable if the slide
      // is divided up into fragments.
      if( currentSlide.querySelectorAll( '.fragment' ).length === 0 ) {
        toArray( currentSlide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
          if( el.hasAttribute( 'data-autoplay' ) ) {
            if( autoSlide && el.duration * 1000 > autoSlide ) {
              autoSlide = ( el.duration * 1000 ) + 1000;
            }
          }
        } );
      }

      // Cue the next auto-slide if:
      // - There is an autoSlide value
      // - Auto-sliding isn't paused by the user
      // - The presentation isn't paused
      // - The overview isn't active
      // - The presentation isn't over
      if( autoSlide && !autoSlidePaused && !isPaused() && !isOverview() && ( !Reveal.isLastSlide() || availableFragments().next || config.loop === true ) ) {
        autoSlideTimeout = setTimeout( navigateNext, autoSlide );
        autoSlideStartTime = Date.now();
      }

      if( autoSlidePlayer ) {
        autoSlidePlayer.setPlaying( autoSlideTimeout !== -1 );
      }

    }

  }

  /**
   * Cancels any ongoing request to auto-slide.
   */
  function cancelAutoSlide() {

    clearTimeout( autoSlideTimeout );
    autoSlideTimeout = -1;

  }

  function pauseAutoSlide() {

    if( autoSlide && !autoSlidePaused ) {
      autoSlidePaused = true;
      dispatchEvent( 'autoslidepaused' );
      clearTimeout( autoSlideTimeout );

      if( autoSlidePlayer ) {
        autoSlidePlayer.setPlaying( false );
      }
    }

  }

  function resumeAutoSlide() {

    if( autoSlide && autoSlidePaused ) {
      autoSlidePaused = false;
      dispatchEvent( 'autoslideresumed' );
      cueAutoSlide();
    }

  }

  function navigateLeft() {

    // Reverse for RTL
    if( config.rtl ) {
      if( ( isOverview() || nextFragment() === false ) && availableRoutes().left ) {
        slide( indexh + 1 );
      }
    }
    // Normal navigation
    else if( ( isOverview() || previousFragment() === false ) && availableRoutes().left ) {
      slide( indexh - 1 );
    }

  }

  function navigateRight() {

    // Reverse for RTL
    if( config.rtl ) {
      if( ( isOverview() || previousFragment() === false ) && availableRoutes().right ) {
        slide( indexh - 1 );
      }
    }
    // Normal navigation
    else if( ( isOverview() || nextFragment() === false ) && availableRoutes().right ) {
      slide( indexh + 1 );
    }

  }

  function navigateUp() {

    // Prioritize hiding fragments
    if( ( isOverview() || previousFragment() === false ) && availableRoutes().up ) {
      slide( indexh, indexv - 1 );
    }

  }

  function navigateDown() {

    // Prioritize revealing fragments
    if( ( isOverview() || nextFragment() === false ) && availableRoutes().down ) {
      slide( indexh, indexv + 1 );
    }

  }

  /**
   * Navigates backwards, prioritized in the following order:
   * 1) Previous fragment
   * 2) Previous vertical slide
   * 3) Previous horizontal slide
   */
  function navigatePrev() {

    // Prioritize revealing fragments
    if( previousFragment() === false ) {
      if( availableRoutes().up ) {
        navigateUp();
      }
      else {
        // Fetch the previous horizontal slide, if there is one
        var previousSlide;

        if( config.rtl ) {
          previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.future' ) ).pop();
        }
        else {
          previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.past' ) ).pop();
        }

        if( previousSlide ) {
          var v = ( previousSlide.querySelectorAll( 'section' ).length - 1 ) || undefined;
          var h = indexh - 1;
          slide( h, v );
        }
      }
    }

  }

  /**
   * The reverse of #navigatePrev().
   */
  function navigateNext() {

    // Prioritize revealing fragments
    if( nextFragment() === false ) {
      if( availableRoutes().down ) {
        navigateDown();
      }
      else if( config.rtl ) {
        navigateLeft();
      }
      else {
        navigateRight();
      }
    }

    // If auto-sliding is enabled we need to cue up
    // another timeout
    cueAutoSlide();

  }


  // --------------------------------------------------------------------//
  // ----------------------------- EVENTS -------------------------------//
  // --------------------------------------------------------------------//

  /**
   * Called by all event handlers that are based on user
   * input.
   */
  function onUserInput( event ) {

    if( config.autoSlideStoppable ) {
      pauseAutoSlide();
    }

  }

  /**
   * Handler for the document level 'keypress' event.
   */
  function onDocumentKeyPress( event ) {

    // Check if the pressed key is question mark
    if( event.shiftKey && event.charCode === 63 ) {
      if( dom.overlay ) {
        closeOverlay();
      }
      else {
        showHelp( true );
      }
    }

  }

  /**
   * Handler for the document level 'keydown' event.
   */
  function onDocumentKeyDown( event ) {

    // If there's a condition specified and it returns false,
    // ignore this event
    if( typeof config.keyboardCondition === 'function' && config.keyboardCondition() === false ) {
      return true;
    }

    // Remember if auto-sliding was paused so we can toggle it
    var autoSlideWasPaused = autoSlidePaused;

    onUserInput( event );

    // Check if there's a focused element that could be using
    // the keyboard
    var activeElementIsCE = document.activeElement && document.activeElement.contentEditable !== 'inherit';
    var activeElementIsInput = document.activeElement && document.activeElement.tagName && /input|textarea/i.test( document.activeElement.tagName );

    // Disregard the event if there's a focused element or a
    // keyboard modifier key is present
    if( activeElementIsCE || activeElementIsInput || (event.shiftKey && event.keyCode !== 32) || event.altKey || event.ctrlKey || event.metaKey ) return;

    // While paused only allow "unpausing" keyboard events (b and .)
    if( isPaused() && [66,190,191].indexOf( event.keyCode ) === -1 ) {
      return false;
    }

    var triggered = false;

    // 1. User defined key bindings
    if( typeof config.keyboard === 'object' ) {

      for( var key in config.keyboard ) {

        // Check if this binding matches the pressed key
        if( parseInt( key, 10 ) === event.keyCode ) {

          var value = config.keyboard[ key ];

          // Callback function
          if( typeof value === 'function' ) {
            value.apply( null, [ event ] );
          }
          // String shortcuts to reveal.js API
          else if( typeof value === 'string' && typeof Reveal[ value ] === 'function' ) {
            Reveal[ value ].call();
          }

          triggered = true;

        }

      }

    }

    // 2. System defined key bindings
    if( triggered === false ) {

      // Assume true and try to prove false
      triggered = true;

      switch( event.keyCode ) {
        // p, page up
        case 80: case 33: navigatePrev(); break;
        // n, page down
        case 78: case 34: navigateNext(); break;
        // h, left
        case 72: case 37: navigateLeft(); break;
        // l, right
        case 76: case 39: navigateRight(); break;
        // k, up
        case 75: case 38: navigateUp(); break;
        // j, down
        case 74: case 40: navigateDown(); break;
        // home
        case 36: slide( 0 ); break;
        // end
        case 35: slide( Number.MAX_VALUE ); break;
        // space
        case 32: isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext(); break;
        // return
        case 13: isOverview() ? deactivateOverview() : triggered = false; break;
        // two-spot, semicolon, b, period, Logitech presenter tools "black screen" button
        case 58: case 59: case 66: case 190: case 191: togglePause(); break;
        // f
        case 70: enterFullscreen(); break;
        // a
        case 65: if ( config.autoSlideStoppable ) toggleAutoSlide( autoSlideWasPaused ); break;
        default:
          triggered = false;
      }

    }

    // If the input resulted in a triggered action we should prevent
    // the browsers default behavior
    if( triggered ) {
      event.preventDefault && event.preventDefault();
    }
    // ESC or O key
    else if ( ( event.keyCode === 27 || event.keyCode === 79 ) && features.transforms3d ) {
      if( dom.overlay ) {
        closeOverlay();
      }
      else {
        toggleOverview();
      }

      event.preventDefault && event.preventDefault();
    }

    // If auto-sliding is enabled we need to cue up
    // another timeout
    cueAutoSlide();

  }

  /**
   * Handler for the 'touchstart' event, enables support for
   * swipe and pinch gestures.
   */
  function onTouchStart( event ) {

    touch.startX = event.touches[0].clientX;
    touch.startY = event.touches[0].clientY;
    touch.startCount = event.touches.length;

    // If there's two touches we need to memorize the distance
    // between those two points to detect pinching
    if( event.touches.length === 2 && config.overview ) {
      touch.startSpan = distanceBetween( {
        x: event.touches[1].clientX,
        y: event.touches[1].clientY
      }, {
        x: touch.startX,
        y: touch.startY
      } );
    }

  }

  /**
   * Handler for the 'touchmove' event.
   */
  function onTouchMove( event ) {

    // Each touch should only trigger one action
    if( !touch.captured ) {
      onUserInput( event );

      var currentX = event.touches[0].clientX;
      var currentY = event.touches[0].clientY;

      // If the touch started with two points and still has
      // two active touches; test for the pinch gesture
      if( event.touches.length === 2 && touch.startCount === 2 && config.overview ) {

        // The current distance in pixels between the two touch points
        var currentSpan = distanceBetween( {
          x: event.touches[1].clientX,
          y: event.touches[1].clientY
        }, {
          x: touch.startX,
          y: touch.startY
        } );

        // If the span is larger than the desire amount we've got
        // ourselves a pinch
        if( Math.abs( touch.startSpan - currentSpan ) > touch.threshold ) {
          touch.captured = true;

          if( currentSpan < touch.startSpan ) {
            activateOverview();
          }
          else {
            deactivateOverview();
          }
        }

        event.preventDefault();

      }
      // There was only one touch point, look for a swipe
      else if( event.touches.length === 1 && touch.startCount !== 2 ) {

        var deltaX = currentX - touch.startX,
          deltaY = currentY - touch.startY;

        if( deltaX > touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
          touch.captured = true;
          navigateLeft();
        }
        else if( deltaX < -touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
          touch.captured = true;
          navigateRight();
        }
        else if( deltaY > touch.threshold ) {
          touch.captured = true;
          navigateUp();
        }
        else if( deltaY < -touch.threshold ) {
          touch.captured = true;
          navigateDown();
        }

        // If we're embedded, only block touch events if they have
        // triggered an action
        if( config.embedded ) {
          if( touch.captured || isVerticalSlide( currentSlide ) ) {
            event.preventDefault();
          }
        }
        // Not embedded? Block them all to avoid needless tossing
        // around of the viewport in iOS
        else {
          event.preventDefault();
        }

      }
    }
    // There's a bug with swiping on some Android devices unless
    // the default action is always prevented
    else if( navigator.userAgent.match( /android/gi ) ) {
      event.preventDefault();
    }

  }

  /**
   * Handler for the 'touchend' event.
   */
  function onTouchEnd( event ) {

    touch.captured = false;

  }

  /**
   * Convert pointer down to touch start.
   */
  function onPointerDown( event ) {

    if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" ) {
      event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
      onTouchStart( event );
    }

  }

  /**
   * Convert pointer move to touch move.
   */
  function onPointerMove( event ) {

    if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" )  {
      event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
      onTouchMove( event );
    }

  }

  /**
   * Convert pointer up to touch end.
   */
  function onPointerUp( event ) {

    if( event.pointerType === event.MSPOINTER_TYPE_TOUCH || event.pointerType === "touch" )  {
      event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
      onTouchEnd( event );
    }

  }

  /**
   * Handles mouse wheel scrolling, throttled to avoid skipping
   * multiple slides.
   */
  function onDocumentMouseScroll( event ) {

    if( Date.now() - lastMouseWheelStep > 600 ) {

      lastMouseWheelStep = Date.now();

      var delta = event.detail || -event.wheelDelta;
      if( delta > 0 ) {
        navigateNext();
      }
      else {
        navigatePrev();
      }

    }

  }

  /**
   * Clicking on the progress bar results in a navigation to the
   * closest approximate horizontal slide using this equation:
   *
   * ( clickX / presentationWidth ) * numberOfSlides
   */
  function onProgressClicked( event ) {

    onUserInput( event );

    event.preventDefault();

    var slidesTotal = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).length;
    var slideIndex = Math.floor( ( event.clientX / dom.wrapper.offsetWidth ) * slidesTotal );

    if( config.rtl ) {
      slideIndex = slidesTotal - slideIndex;
    }

    slide( slideIndex );

  }

  /**
   * Event handler for navigation control buttons.
   */
  function onNavigateLeftClicked( event ) { event.preventDefault(); onUserInput(); navigateLeft(); }
  function onNavigateRightClicked( event ) { event.preventDefault(); onUserInput(); navigateRight(); }
  function onNavigateUpClicked( event ) { event.preventDefault(); onUserInput(); navigateUp(); }
  function onNavigateDownClicked( event ) { event.preventDefault(); onUserInput(); navigateDown(); }
  function onNavigatePrevClicked( event ) { event.preventDefault(); onUserInput(); navigatePrev(); }
  function onNavigateNextClicked( event ) { event.preventDefault(); onUserInput(); navigateNext(); }

  /**
   * Handler for the window level 'hashchange' event.
   */
  function onWindowHashChange( event ) {

    readURL();

  }

  /**
   * Handler for the window level 'resize' event.
   */
  function onWindowResize( event ) {

    layout();

  }

  /**
   * Handle for the window level 'visibilitychange' event.
   */
  function onPageVisibilityChange( event ) {

    var isHidden =  document.webkitHidden ||
            document.msHidden ||
            document.hidden;

    // If, after clicking a link or similar and we're coming back,
    // focus the document.body to ensure we can use keyboard shortcuts
    if( isHidden === false && document.activeElement !== document.body ) {
      // Not all elements support .blur() - SVGs among them.
      if( typeof document.activeElement.blur === 'function' ) {
        document.activeElement.blur();
      }
      document.body.focus();
    }

  }

  /**
   * Invoked when a slide is and we're in the overview.
   */
  function onOverviewSlideClicked( event ) {

    // TODO There's a bug here where the event listeners are not
    // removed after deactivating the overview.
    if( eventsAreBound && isOverview() ) {
      event.preventDefault();

      var element = event.target;

      while( element && !element.nodeName.match( /section/gi ) ) {
        element = element.parentNode;
      }

      if( element && !element.classList.contains( 'disabled' ) ) {

        deactivateOverview();

        if( element.nodeName.match( /section/gi ) ) {
          var h = parseInt( element.getAttribute( 'data-index-h' ), 10 ),
            v = parseInt( element.getAttribute( 'data-index-v' ), 10 );

          slide( h, v );
        }

      }
    }

  }

  /**
   * Handles clicks on links that are set to preview in the
   * iframe overlay.
   */
  function onPreviewLinkClicked( event ) {

    if( event.currentTarget && event.currentTarget.hasAttribute( 'href' ) ) {
      var url = event.currentTarget.getAttribute( 'href' );
      if( url ) {
        showPreview( url );
        event.preventDefault();
      }
    }

  }

  /**
   * Handles click on the auto-sliding controls element.
   */
  function onAutoSlidePlayerClick( event ) {

    // Replay
    if( Reveal.isLastSlide() && config.loop === false ) {
      slide( 0, 0 );
      resumeAutoSlide();
    }
    // Resume
    else if( autoSlidePaused ) {
      resumeAutoSlide();
    }
    // Pause
    else {
      pauseAutoSlide();
    }

  }


  // --------------------------------------------------------------------//
  // ------------------------ PLAYBACK COMPONENT ------------------------//
  // --------------------------------------------------------------------//


  /**
   * Constructor for the playback component, which displays
   * play/pause/progress controls.
   *
   * @param {HTMLElement} container The component will append
   * itself to this
   * @param {Function} progressCheck A method which will be
   * called frequently to get the current progress on a range
   * of 0-1
   */
  function Playback( container, progressCheck ) {

    // Cosmetics
    this.diameter = 50;
    this.thickness = 3;

    // Flags if we are currently playing
    this.playing = false;

    // Current progress on a 0-1 range
    this.progress = 0;

    // Used to loop the animation smoothly
    this.progressOffset = 1;

    this.container = container;
    this.progressCheck = progressCheck;

    this.canvas = document.createElement( 'canvas' );
    this.canvas.className = 'playback';
    this.canvas.width = this.diameter;
    this.canvas.height = this.diameter;
    this.context = this.canvas.getContext( '2d' );

    this.container.appendChild( this.canvas );

    this.render();

  }

  Playback.prototype.setPlaying = function( value ) {

    var wasPlaying = this.playing;

    this.playing = value;

    // Start repainting if we weren't already
    if( !wasPlaying && this.playing ) {
      this.animate();
    }
    else {
      this.render();
    }

  };

  Playback.prototype.animate = function() {

    var progressBefore = this.progress;

    this.progress = this.progressCheck();

    // When we loop, offset the progress so that it eases
    // smoothly rather than immediately resetting
    if( progressBefore > 0.8 && this.progress < 0.2 ) {
      this.progressOffset = this.progress;
    }

    this.render();

    if( this.playing ) {
      features.requestAnimationFrameMethod.call( window, this.animate.bind( this ) );
    }

  };

  /**
   * Renders the current progress and playback state.
   */
  Playback.prototype.render = function() {

    var progress = this.playing ? this.progress : 0,
      radius = ( this.diameter / 2 ) - this.thickness,
      x = this.diameter / 2,
      y = this.diameter / 2,
      iconSize = 14;

    // Ease towards 1
    this.progressOffset += ( 1 - this.progressOffset ) * 0.1;

    var endAngle = ( - Math.PI / 2 ) + ( progress * ( Math.PI * 2 ) );
    var startAngle = ( - Math.PI / 2 ) + ( this.progressOffset * ( Math.PI * 2 ) );

    this.context.save();
    this.context.clearRect( 0, 0, this.diameter, this.diameter );

    // Solid background color
    this.context.beginPath();
    this.context.arc( x, y, radius + 2, 0, Math.PI * 2, false );
    this.context.fillStyle = 'rgba( 0, 0, 0, 0.4 )';
    this.context.fill();

    // Draw progress track
    this.context.beginPath();
    this.context.arc( x, y, radius, 0, Math.PI * 2, false );
    this.context.lineWidth = this.thickness;
    this.context.strokeStyle = '#666';
    this.context.stroke();

    if( this.playing ) {
      // Draw progress on top of track
      this.context.beginPath();
      this.context.arc( x, y, radius, startAngle, endAngle, false );
      this.context.lineWidth = this.thickness;
      this.context.strokeStyle = '#fff';
      this.context.stroke();
    }

    this.context.translate( x - ( iconSize / 2 ), y - ( iconSize / 2 ) );

    // Draw play/pause icons
    if( this.playing ) {
      this.context.fillStyle = '#fff';
      this.context.fillRect( 0, 0, iconSize / 2 - 2, iconSize );
      this.context.fillRect( iconSize / 2 + 2, 0, iconSize / 2 - 2, iconSize );
    }
    else {
      this.context.beginPath();
      this.context.translate( 2, 0 );
      this.context.moveTo( 0, 0 );
      this.context.lineTo( iconSize - 2, iconSize / 2 );
      this.context.lineTo( 0, iconSize );
      this.context.fillStyle = '#fff';
      this.context.fill();
    }

    this.context.restore();

  };

  Playback.prototype.on = function( type, listener ) {
    this.canvas.addEventListener( type, listener, false );
  };

  Playback.prototype.off = function( type, listener ) {
    this.canvas.removeEventListener( type, listener, false );
  };

  Playback.prototype.destroy = function() {

    this.playing = false;

    if( this.canvas.parentNode ) {
      this.container.removeChild( this.canvas );
    }

  };


  // --------------------------------------------------------------------//
  // ------------------------------- API --------------------------------//
  // --------------------------------------------------------------------//


  Reveal = {
    initialize: initialize,
    configure: configure,
    sync: sync,

    // Navigation methods
    slide: slide,
    left: navigateLeft,
    right: navigateRight,
    up: navigateUp,
    down: navigateDown,
    prev: navigatePrev,
    next: navigateNext,

    // Fragment methods
    navigateFragment: navigateFragment,
    prevFragment: previousFragment,
    nextFragment: nextFragment,

    // Deprecated aliases
    navigateTo: slide,
    navigateLeft: navigateLeft,
    navigateRight: navigateRight,
    navigateUp: navigateUp,
    navigateDown: navigateDown,
    navigatePrev: navigatePrev,
    navigateNext: navigateNext,

    // Forces an update in slide layout
    layout: layout,

    // Returns an object with the available routes as booleans (left/right/top/bottom)
    availableRoutes: availableRoutes,

    // Returns an object with the available fragments as booleans (prev/next)
    availableFragments: availableFragments,

    // Toggles the overview mode on/off
    toggleOverview: toggleOverview,

    // Toggles the "black screen" mode on/off
    togglePause: togglePause,

    // Toggles the auto slide mode on/off
    toggleAutoSlide: toggleAutoSlide,

    // State checks
    isOverview: isOverview,
    isPaused: isPaused,
    isAutoSliding: isAutoSliding,

    // Adds or removes all internal event listeners (such as keyboard)
    addEventListeners: addEventListeners,
    removeEventListeners: removeEventListeners,

    // Facility for persisting and restoring the presentation state
    getState: getState,
    setState: setState,

    // Presentation progress on range of 0-1
    getProgress: getProgress,

    // Returns the indices of the current, or specified, slide
    getIndices: getIndices,

    getTotalSlides: getTotalSlides,

    // Returns the slide element at the specified index
    getSlide: getSlide,

    // Returns the slide background element at the specified index
    getSlideBackground: getSlideBackground,

    // Returns the previous slide element, may be null
    getPreviousSlide: function() {
      return previousSlide;
    },

    // Returns the current slide element
    getCurrentSlide: function() {
      return currentSlide;
    },

    // Returns the current scale of the presentation content
    getScale: function() {
      return scale;
    },

    // Returns the current configuration object
    getConfig: function() {
      return config;
    },

    // Helper method, retrieves query string as a key/value hash
    getQueryHash: function() {
      var query = {};

      location.search.replace( /[A-Z0-9]+?=([\w\.%-]*)/gi, function(a) {
        query[ a.split( '=' ).shift() ] = a.split( '=' ).pop();
      } );

      // Basic deserialization
      for( var i in query ) {
        var value = query[ i ];

        query[ i ] = deserialize( unescape( value ) );
      }

      return query;
    },

    // Returns true if we're currently on the first slide
    isFirstSlide: function() {
      return ( indexh === 0 && indexv === 0 );
    },

    // Returns true if we're currently on the last slide
    isLastSlide: function() {
      if( currentSlide ) {
        // Does this slide has next a sibling?
        if( currentSlide.nextElementSibling ) return false;

        // If it's vertical, does its parent have a next sibling?
        if( isVerticalSlide( currentSlide ) && currentSlide.parentNode.nextElementSibling ) return false;

        return true;
      }

      return false;
    },

    // Checks if reveal.js has been loaded and is ready for use
    isReady: function() {
      return loaded;
    },

    // Forward event binding to the reveal DOM element
    addEventListener: function( type, listener, useCapture ) {
      if( 'addEventListener' in window ) {
        ( dom.wrapper || document.querySelector( '.reveal' ) ).addEventListener( type, listener, useCapture );
      }
    },
    removeEventListener: function( type, listener, useCapture ) {
      if( 'addEventListener' in window ) {
        ( dom.wrapper || document.querySelector( '.reveal' ) ).removeEventListener( type, listener, useCapture );
      }
    },

    // Programatically triggers a keyboard event
    triggerKey: function( keyCode ) {
      onDocumentKeyDown( { keyCode: keyCode } );
    }
  };

  return Reveal;

}));
